Manual
342.1214.02
1. | Data sheet | |||
---|---|---|---|---|
Characteristics | ||||
Specifications | ||||
2. | Preparation for Use and Operating Instructions | 2.1 | ||
2.1 | Key to Front- and Rear-panel Views | 2.1 | ||
2.2 | Preparation for Use | 2.4 | ||
2.2.1 | Setting Up the Voltmeter | 2.4 | ||
2.2.2 | Rack-mounting the Voltmeter | 2.4 | ||
2.2.3 | Power Supply | 2.4 | ||
2.2.4 | Switching On | 2.5 | ||
2.3 | Operating Instructions | 2.6 | ||
2.3.1 | Connecting the Voltage to be Measured | 2.6 | ||
2.3.2 | Permissible Input Voltages | 2.7 | ||
2.3.3 | Setting the Voltmeter | 2.7 | ||
2.3.3.1 | Measurement Modes | 2.7 | ||
2.3.3.1.1 | AC Measurements 2. | |||
2.3.3.1.2 | DC Measurements | 2.8 | ||
2.3.3.1.3 | AC+DC Measurement | 2.9 | ||
2.3.3.2 | Display of Measured Value | 2.9 | ||
2.3.3.2.1 | Indicating Modes V, dBV and dBm | 2.10 | ||
2.3.3.2.2 | Relative Indication (AV, A%, AdB, V/REF) | 2.10 | ||
2.3.3.2.3 | Tendency Indication | 2.11 | ||
2.3.3.3 | Indication of Reference Voltage and Reference Impedance | 2.11 | ||
2.3.3.4 | Measurement Speed | 2.12 | ||
2.3.3.5 | Switchable Low-pass Filter | 2.13 | ||
2.3.3.6 | Switching off Autoranging | 2.14 | ||
2.3.3.7 | Second Functions | 2.15 | ||
2.3.3.7.1 | Entry of Reference Voltage and Reference Impedance | 2.15 | ||
2.3.3.7.2 | Service Functions | 2.18 | ||
2.3.3.8 | Basic Setting | 2.20 | ||
2.3.3.9 | Error Messages | 2.21 | ||
2.3.4 | IEC-bus Control of the URE | 2.21 | ||
2.3.4.1 | Setting the Device Address/Talk Only Mode | 2.22 | ||
2.3.4.2 | Interface Functions | 2.23 |
2.3.4.3 | Device IEC-bus Instructions | 2.23 |
---|---|---|
2.3.4.3.1 | Setting Instructions | 2.24 |
2.3.4.3.2 | Data Entry Instructions (Table 2-6) | 2.26 |
2.3.4.3.3 | Interface Instructions (Table 2-7) | 2.26 |
2.3.4.3.4 | Device Trigger Instructions (Tables 2-8 and 2-9) | 2.26 |
2.3.4.3.5 | Service Instructions (Table 2-9) | 2.27 |
2.3.4.4 | Data Output | 2.31 |
2.3.4.5 | Group of Addressed and Universal Instructions | 2.32 |
2.3.4.5.1 | Remote/Local | 2.32 |
2.3.4.5.2 | Device Clear | 2.33 |
2.3.4.5.3 | Device Trigger | 2.33 |
2.3.4.5.4 | Service Request | 2.33 |
2.3.4.5.5 | Notes for CEM Computer Users | 2.34 |
2.3.4.6 | Data Output in Talk Only Mode | 2.37 |
2.3.4.7 | Retrofitting the IEC-bus Option | 2.37 |
2.3.5 | Analog Output | 2.38 |
2.3.5.1 | Retrofitting the Analog Output Option | 2.39 |
-
Table of Contents
3. | Maintenance |
---|---|
3.1 | Measuring Equipment Required 3.1 |
3.2 | Check of Voltmeter Operation |
3.2.1 | Check of Display and Key Functions |
3.2.1.1 | Displays |
3.2.1.2 | Keys |
3.2.2 | Check of AC Measurement Characteristics |
3.2.2.1 |
Error Limits in Voltage Measurements at Lower
Frequencies |
3.2.2.2 |
Error Limits in Voltage Measurements at Higher
Frequencies |
3.2.2.3 | Switchable Low-pass Filter 3.8 |
3.2.2.4 | Speed Selection of AC Measurements |
3.2.2.5 | Measurement Rectifier |
3.2.2.5.1 | Linearity of Measured Values |
3.2.2.5.2 | Error Limits in RMS Measurements 3.12 |
3.2.3 | Check of DC Measurement Characteristics |
3.2.3.1 | Error Limits in DC Voltage Measurements |
3.2.3.2 | Speed Selection of DC Measurements and AC Suppression 3.15 |
3.2.4 | Check of AC+DC Measurement Characteristics 3.16 |
3.2.5 | Check of Input Impedance 3.16 |
3.2.6 | Check of Relative Functions 3.17 |
3.2.6.1 | Storage of Reference Value and Reference Impedance 3.17 |
3.2.6.2 | Check of dBm, dBV and AdB ranges 3.18 |
3.2.7 | Check of IEC-bus Interface 3.19 |
3.2.8 | Check of Analog Output 3.20 |
3.3 | Electrical Maintenance 3.20 |
3.3.1 | Autocalibration |
3.3.2 | Check of Lithium Buffer Battery 3.22 |
3.3.3 | Check of Reference Voltages 3.22 |
3.4 | Mechanical Maintenance 3.23 |
3.5 | Storage |
4. | Functional Description | 4.1 |
---|---|---|
4.1 | Overall Function | 4.1 |
4.2 | Computer Board | 4.4 |
4.2.1 | Power Supply | 4.7 |
4.2.2 | IEC-bus Interface | 4.7 |
4.2.3 | Signature Analysis | 4.8 |
4.2.4 | Analog Output | 4.9 |
4.3 | Display Board | 4.9 |
4.4 | Analog Board | 4.10 |
4.4.1 | Switching Functions | 4.10 |
4.4.1.1 | Input Switchover | 4.11 |
4.4.1.2 | Input Amplifier | 4.11 |
4.4.1.3 | Range Divider | 4.12 |
4.4.1.4 | Buffer Amplifier | 4.12 |
4.4.1.5 | Low-pass-filter Selection | 4.12 |
4.4.1.6 | High-pass-filter Selection | 4.12 |
4.4.1.7 | Push-pull Amplifier | 4.12 |
4.4.1.8 | Measurement Rectifier with Filter Circuits | 4.14 |
4.4.1.9 | DC Amplifier | 4.15 |
4.4.1.10 | Microprocessor-controlled A/D Conversion | 4.15 |
4.4.1.11 | DC and AC Reference Voltages | 4.16 |
4.4.1.12 | Transmission and Decoding of the Analog Control Signals | 4.17 |
4.4.1.13 | Activation of Analog Switching Functions | 4.18 |
4.4.2 | Function Sequence | 4.18 |
4.4.2.1 | Autocalibration | 4.19 |
4.4.2.2 | RMS-value Measurement and Rectifier Calibration | 4.20 |
4.4.2.3 | DC Voltage Measurements and Offset Correction | 4.21 |
4.4.2.4 | Mixed (AC+DC) Voltage Measurements | 4.22 |
4.4.2.5 | Automatic Range Selection and RANGE HOLD | 4.23 |
Table of Contents
5. | Repair | 5.1 | |
---|---|---|---|
5.1 | Equipment Required | 5.1 | |
5.2 | Troubleshooting | 5.1 | |
5.2.1 | Servicing Aids | 5.1 | |
5.2.1.1 | Service Functions 5 to 9 | 5.1 | |
5.2.1.2 | Error Messages and Evaluation | 5.3 | |
5.2.1.3 | Error Symptoms | 5.5 | |
5.2.2 | Troubleshooting and Check of Power Supply | 5.6 | |
5.2.3 | Troubleshooting and Check of Computer Board | 5.6 | |
5.2.3.1 | Check of Supply Voltages | 5.7 | |
5.2.3.2 | Check of Microprocessor and Peripheral Units | 5.9 | |
5.2.4 | Troubleshooting and Check of IEC-bus Interface | 5.12 | |
* | 5.2.5 | Troubleshooting and Check of Analog Output | 5.12 |
5.2.6 | Troubleshooting and Check of Display Board | 5.13 | |
5.2.7 | Troubleshooting and Check of Analog Board | 5.14 | |
5.2.7.1 |
Check of Interface Functions
Analog/Computer Sections |
5.14 | |
5.2.7.2 | Check of Input Circuit and Input Amplifier | 5.15 | |
5.2.7.3 | Check of Range Divider and Buffer Amplifier | 5.16 | |
5.2.7.4 | Check of Push-pull Amplifier | 5.16 | |
5.2.7.5 | Check of RMS-value Rectifier | 5.17 | |
5.2.7.6 | Check of DC-Amplifier Branch | 5.18 | |
5.2.7.7 | Check of Reference Voltages | 5.20 | |
5.3 | Adjustment of the URE | 5.21 | |
5.3.1 | Adjustment of the Analog Board | 5.21 | |
0 | 5.3.1.1 | Adjustment of Reference Voltages | 5.21 |
5.3.1.2 | Rectifier Adjustment | 5.23 | |
5.3.1.2.1 | Offset Adjustment of Push-pull Amplifier | 5.23 | |
5.3.1.2.2 | Balance Adjustment | 5.23 | |
5.3.1.2.3 | Adjustment of Rectifier Amplifier | 5.23 | |
5.3.1.3 | Adjustment of 1-dB Input Divider | 5.24 | |
5.3.1.4 | Absolute-value Adjustment of AC Indication | 5.24 | |
5.3.1.5 | Adjustment of Frequency Characteristic | 5.25 | |
5.3.2 | Adjustment of Analog Output | 5.27 | |
5.4 | Spare Parts | 5.27 |
Supplement to Manual 342.2704 URE 342.1214.02
Change data of DC Output Option URE-B2 to read as follows:
Error limits ..... ± 2 mV
RMS VOLTMETER URE
AC (10 Hz to 10 MHz): 50 µV to 300 V DC: 0 to ±300 V
𝐼 RMS-VOLTMETER
(IEC 625 Bus
342 1214 02
The RMS Voltmeter URE uses an rms-value rectifier circuit of new design and permits true rms-value measurement with wide bandwidth and both high measurement speed and accuracy. A microprocessor provides for error correction and converts the measured values for readout in different selectable units. The IEC-bus interface option permits the use of the URE in automatic test assemblies.
Measured quantities. The URE measures DC voltages and the rms value of AC and AC + DC voltages in the frequency range from 10 Hz to 10 MHz (typical range limit at 20 MHz). For AC + DC voltage measurements the microprocessor measures alternately the DC and the AC voltage and determines the total rms value by square-law addition of the individual components.
Measurement speed. The URE provides three different measurement speeds: SLOW, FAST and SUPERFAST (1/ 3/30 measurements per second). The FAST button is for switchover between SLOW and FAST. SUPERFAST can be selected via the IEC bus or with the aid of service function 3. The lower cutoff frequency of the URE is matched to the selected measurement rate by automatically switched highpass filters in the AC measuring circuit. Hence, low-frequency AC voltages can only be measured at a slow rate, and the DC measuring circuit suppresses AC voltages the better, the lower the measurement rate selected.
Measuring functions. The AC, DC and AC + DC buttons permit selection of AC, DC or AC + DC measurement. The measured values are read out in V or mV and autoranging is enabled.
DC measurement. In this switch position the URE measures the DC voltage component up to a maximum of ± 300 V with a resolution of 1 µV in the most sensitive measurement range. A higher-order lowpass filter automatically selected with the measurement speed suppresses superimposed AC voltages.
AC measurement. In this mode the RMS Voltmeter measures the rms value of AC voltages in the range from 50 µV to 300 V at crest factors of up to 5. The frequency range is 10 Hz to 10 MHz (typ. 20 MHz), the lower cutoff frequency as a function of the measurement rate is 10 Hz, 100 Hz or 1 kHz. For suppression of unwanted frequencies the upper cutoff frequency can be limited to 100 kHz, 20 kHz or 4 kHz with the aid of a built-in lowpass filter. The filter is switched in with the LOWPASS button, the cutoff frequency of the filter is selected with the SELECT button.
AC + DC measurement. For AC + DC measurements the URE carries out alternately an AC and a DC measurement and reads out the total rms value of the AC + DC voltage. Voltage components whose frequencies are less than the lower cutoff frequency of the AC measuring circuit are not fully considered. Measurement range and bandwidth are as described under DC and AC measurement.
Blue: second functions
Display of measured value. The display panel of the URE is subdivided into several sections (see photo on the left). The measured value is read out on a 41/2-digit 7-segment LED display and the associated unit by luminous letters arranged next to it. If the numerical value is positive the sign is blanked. Blinking of the display shows that the result is invalid, e.g. because the range is exceeded. If the measured value is below the range, only the last digit blinks.
For quick detection of any changes in the measured value the URE has a tendency indication which also facilitates adjustments and maximum/minimum settings. It consists of LEDs arranged in a circle, the lighted LED corresponding to the momentary measured value. If the measured value becomes higher or lower this light dot follows quasianalogously clockwise or counterclockwise. The two illuminated displays on the right indicate the selected cutoff frequency of the lowpass filter for AC measurements and the current remote control status of the URE.
Conversion of measured value. The microprocessor of the URE converts the measured values, if desired, at the push of a button for readout in different units.
The following readouts can be selected:
Unit | Button | |||
---|---|---|---|---|
• | Voltage | V or mV | V | |
• | Level | dBV | dBV | |
• | Power level (referred to reference | 016 C 1924 | ||
impedance entered) | dBm | dBm(Z) | ||
Voltage deviation | ||||
from reference value | V or mV | ΔV | ||
• | Relative voltage deviation | |||
from reference value in dB | dB | ΔdB | ||
• | Relative voltage deviation | |||
from reference value in % | % | Δ% | ||
• | Ratio of measured value | |||
to reference value | - | V/REF |
A | so indicated are: | Unit | Button | |
---|---|---|---|---|
• | Stored reference value | V, mV, | RCL | |
dBV, dBm | REF | |||
• | Stored reference impedance | |||
for power level measurement | Ω | RCL Z |
Reference values may be entered from 1 μV to 19999 V, reference impedances from 0.1 mΩ to 19999 Ω. The measured value can also directly be used as reference value. The table below shows in detail the many ways of displaying the results in the RMS Voltmeter URE.
Service functions. The service functions of the URE are only rarely required and therefore no separate buttons are provided for them. These functions can be called up by pressing a certain combination of buttons. The functions display test, display of IEC-bus address or autocalibration, for instance, can easily be executed by entering a code number via the keyboard.
IEC-bus Option URE-B1. This option permits all functions of the voltmeter to be remotely controlled. The maximum measurement speed of 30 measurements per second makes the URE an ideal AF system voltmeter.
DC Output Option URE-B2. This output supplies a DC voltage proportional to the indicated numerical value which permits logging of the measured values on a recorder. Thanks to the manifold conversion capabilities of the URE the scale can be linear or logarithmic. The output voltage range is -2 V to +2 V with least increments of 1 mV.
The relationship between the analog output voltage and the measured value is as follows:
Output
voltage |
Readout without
decimal point |
Example:
Readout |
V
out
+ 1.150 V ' - 0.372 V |
---|---|---|---|
v | 10 000 |
|
|
1.13% | + 0.011 V |
Measured values /conversion
Voltage Level Button: dBV dBm (Z) V/mV |
Reference values 1 ) | Deviations from reference value | ||||||
---|---|---|---|---|---|---|---|---|
Voltage
Button: V/mV |
STO |
V/mV, dBV/
dBm; STO |
ΔV | ΔdB | Δ% | V/REF | ||
10.000 V
1.0000 V |
20.00 dBV
.00 dBV |
33.01 dBm
13.01 dBm - 65.05 dBm |
50.00 Ω | 1.0000 V |
9.000 V
0. V -0.999 V |
20.00 dB
0. dB 78.06 dB |
900.0 %
0. % 99.98 % |
10.000
1.0000 .0001 |
1.0000 V
1.0000 V 1.0000 V |
.00 dBV
.00 dBV .00 dBV |
12.22 dBm
11.25 dBm 6.20 dBm |
60.00 Ω
75.00 Ω 240.0 Ω |
.1000 mV |
.9999 V
.9999 V .9999 V |
80.00 dB
80.00 dB 80.00 dB |
19999 %
19999 % 19999 % |
10000
10000 10000 |
10.000 V
2 400 V |
20.00 dBV
7.60 dBV |
22.22 dBm
9.81 dBm |
600.0 Ω |
.0010 mV
. 7750 V |
10.000 V
1.625 V |
140.00 dB
2
)
9.81 dB |
19999 %
209.7 % |
19999
3.097 |
10.000 V
12.57 V 2.236 V 25.00 V |
20.00 dBV
21.99 dBV 6.99 dBV 27.96 dBV |
10.00 dBm
35.00 dBm 20.00 dBm 40.96 dBm |
10000 Ω
50.00 Ω |
1.0000 V
20.00 dBV 20.00 dBm 10.00 dBm |
9.000 V
2.570 V 0. V 24.29 V |
20.00 dB
1.99 dB 0. dB 30.96 dB |
900.0 %
25.70 % 0. % 3436 % |
10.00
1.2570 1.0000 35.36 |
Entered value or measured value used; values remain stored until new value is entered.
2) dBµV.
atus
LY
d + 30 to + 45°C) + 1 digit)/°C
II operating modes T5, L4, SR1, RL1,
dew a 0°C 20/240 V ±10%, : (35 VA)
078.8222.00
iss 1 to
A) m × 340 mm, 4,4 kg
tions | Readout of measured values | |
Units of measured parameters V or mV | ||
(see also text) dBV | ||
dBm | ||
ΔV or ΔmV | ||
ameters | . DC voltage | ΔdB, Δ% |
AC voltage | ratio (without unit) | |
AC + DC voltage | Measured value, digital | |
Tendency indication guasi-analog indication | ||
dot travelling in a circle | ||
without lowpass | Resolution in lowest sub- | |
. 10 Hz to 10 MHz (typ. up to 20 MHz) | rance | |
ncy (-3 dB) of | Digital steps | |
ed lowpass | ||
. 4/20/100 kHz, | Error limits (at tamb + 15 to + 30°C) | |
40 dB/decade | DC 0.1% of rdg + 10 digits | |
AC (crest factor <3) see table below | ||
ranyes | AC + DC (crest factor <3) see table below, | |
. 0 to ± 300 V | plus 10 digits | |
. 50 μV to 300 V | Additional error at crest | |
**************** | automatic or manual | factor 3 to 5 3% of rdg |
. when applying the test voltage, | ||
with optimum switching speed | Temperature effect (at tamb + 5 to + 15 and + 30 to + 45° | |
. with RANGE HOLD button: | DC (0.01% of rdg + 1 digit | |
prevents autoranging from | AC, up to 1 MHz 0.05% of rdg/°C | |
switching to a lower range | up to 10 MHz 0.15% of rdg/°C | |
or | ||
selection of any range via | Data of options | |
service function | Data of options | |
BNC female, floating | IEC-bus Option URE-B1 | |
10 MO shupted by <40 pE | Interface to IEC 625-1 standard for control of all operating | |
situ un to 20 kl/z | V - 600 V V - 300 V | Interface functions |
V = 250 V V = 200 V | DC1. DT1 | |
up to 500 kHz | Connector | |
above 500 kHz . |
. Vrms X1= \10. V X112 <40 V (chock hozard) |
|
-mode voltage | . <42 V (SHOCK Hazard) | DC Output Option URE-B2 |
le rejection | , >120 dB up to 100 Hz | Output impedance |
>100 dB up to 10 kHz | Output voltage range2 to +2 V | |
Resolution | ||
rate (measure- | AC DC ACIDC | Error limits |
1) | AC DC AC+DC | |
Hz) | . 0.8 0.8 0.4 | General data |
Hz) | . 3 3 1.5 | |
(f) = 1 kHz) | . 30 30 15 | Operating temperature range + 5 to + 45°C, salety C |
to 0.1% of fsd | IEC 359 (no dew accun | |
ging the range) | Storage temperature range40 to + 70°C | |
.1.38 | Power supply | |
. 270 ms | 4/ 10 03 HZ (35 VA) | |
. 25 ms | Dimensions, weight 220 mm x 109 mm x 34 | |
true rms.value rectification | ||
Ordering information | ||
tor | . 5 | |
entered via keyboard or | Order designation RMS Voltmeter URE | |
directly as measured value | 342.1214.02 | |
nee impedance | via kouboard | |
nce impedance | range 0.0001 to 19999 O | Options |
surement) | Tange 0.0001 10 19999 12 | IEC-bus Option URE-B1 342.2910.02 |
* This additional error is almost negligible when the lowpass filter i switched into circuit or when consider the URE. ring the calculated inherent noise of
Recommended extras 19" Rack Adapter ZZA-22 .
MADE IN GERMANY -
Specifica Basic ur
Automatic filter measurement with RMS Voltmeter URE (centre top), Generator SPN (centre bottom) and Process Controller PUC (on the right); on the left: Triple DC Power Supply NGT 20
(See Figs. 2-9 and 2-10 in the appendix)
The values specified in this section are not guaranteed values. The specifications given in the Data Sheet or Technical Information are binding.
Ref. No. | Labelling | Function |
---|---|---|
1 | 4 1/2-digit LED display | |
2 |
mV △
V % dBm dB dBV Ω |
Illuminated display of the unit.
△ lights up during relative measurements |
3 | · | Tendency indication for quick detection of changes in the measured value. |
4 |
LP/kHz
4 20 100 |
Illuminated display of low-pass filter
cut-off frequency |
5 |
REM
LIS TAL SRQ |
Illuminated display of Remote status.
LIS: Listener address TAL: Talker address SRQ: Service Request |
6 |
LOCAL
STO |
Key to interrupt Remote status and for
data output in Talk Only mode. Second function: To store reference voltage or reference impedance. |
7 |
LOWPASS
V/mV SELECT dBm/dBV |
Illuminated key for cutting low-pass
filter into AC measuring circuit. Second function: To enter unit, V or mV, of reference voltage. Key for selection of cut-off frequency. Second function: To enter unit, dBm or dBV, of reference voltage. |
8 |
FAST f > 100 Hz
Ω |
Illuminated key for selecting measure-
ment speed. AC and AC + DC measurement at FAST measu- rement speed possible only if f > 100 Hz. Second function: To enter unit, ohms (Ω), of reference impedance. |
1001 | 100100 | |||||
---|---|---|---|---|---|---|
2 1 | Vor | + ~ | Enent | and | Doom manal | TTJ COLOR |
C | nev | 60 | FFORG | and | near-paner | VIEWS |
and the second se |
Ref. No. | Labelling | Function |
---|---|---|
9 |
RANGE HOLD
CLEAR |
Illuminated key to maintain measurement range selected by autoranging. |
Second function:
Clear key for data entry. |
||
10 | SHIFT | Illuminated key to select second key functions. |
11 |
RCL REFA
+/- |
Illuminated key to call up stored
reference value. Second function: To select sign for data entry. |
12 | Keys for relative indications. | |
∆
v
9 |
Indication of difference between measured and reference voltage. | |
AdB
0 |
Indication of difference between measured and reference voltage in dB. | |
∆%
6 |
Indication of difference between measured and reference voltage in %. | |
V/REF
• |
Indication of ratio of measured to reference voltage. | |
Second functions:
Digits 9, 0, 6 and decimal point for data entry. |
||
13 |
RCL Z
3 |
Illuminated key to call up reference
impedance. Second function: Digit 3 for data entry. |
14 | Keys to select unit of measured voltage. | |
V
8 |
Indication in V or mV. | |
dBV
5 |
Indication in dBV. | |
dBm(Z)
2 |
Indication in dEm.
Z: reference impedance. |
|
Second functions:
Digits 8, 5, 2 for data entry. |
||
15 | Illuminated keys to select measuring mode. | |
AC
7 |
AC measurement | |
DC
4 |
DC measurement | |
AC + DC | AC + DC measurement | |
Second functions:
Digits 7, 4, 1 for data entry. |
Ref. No. | Labelling | Function |
---|---|---|
16 |
INPUT
10 MΩ < 40 pF |
Input socket |
17 | Light bar to indicate SUPERFAST measurement speed. | |
18 |
ON
POWER OFF |
Power switch |
19 | ±2 ∞ ↔ | Analog output |
20 |
ADDRESS
O TALK ONLY I NORMAL A5A1 |
Address switch for IEC-bus interface.
Talk Only mode selector. |
21 | IEC bus connector | |
22 | ( + ) 47 - 63 Hz | AC supply receptacle |
23 |
100 V/120 V
T0.5B 200 V/240 V T0.25B |
Fuse holder/voltage selector |
The URE may be operated in any position. For ease of operation and to facilitate reading the displays, it is best to tilt the voltmeter slightly. For this purpose, press the two ends of the carrying handle together near the pivot, adjust the handle to the desired position and release the handle to let it lock in place.
The URE is designed for operation at an ambient temperature from +5°C to +45°C. The ventilation holes in the top and underside of the URE must not be obstructed. Water must not be allowed to condense on the URE. If this has occurred, the URE must be allowed to dry before it is switched on.
The URE can be mounted in 19" racks with use of Adapter ZZA-22 (see "Recommended Extras"). For such mounting, the two covers are replaced by special covers, the carrying handle and the two side strips are removed and a dummy section is screwed to the left-hand or right-hand side of the URE to produce a mountable unit.
The URE is designed for operation with AC supply voltages of 100 V, 120 V, 220 V or 240 V +10% and frequencies between 47 and 63 Hz. The voltmeter is factory-adjusted for operation by 220 V but is readily adapted for one of the other supplies by lifting off the cover of the fuse holder 22 with a screwdriver, exchanging the fuse if necessary and replacing the cover so that the triangular marker points to the desired voltage (Fig. 2-14 in the appendix). For 220 V and 240 V, insert fuse T0,25B DIN 41571 and for 100 V and 120 V, fuse T0,5B DIN 41571.
Connect the URE to the power outlet via the AC supply receptacle with the power cord supplied. The URE complies with the provisions of VDE 0411 Safety Class I. For safety
connect the URE only to an outlet with a non-fused ground contact.
Switch on the URE by means of the power switch on the rear panel of the instrument. The display will read
and subsequently the device address for the IEC-bus connector, for example
for address 7, or, in the Talk Only mode
(see section 2.3.4.1).
If the IEC-bus option (Recommended extras) is not incorporated, the display reads
The instrument then assumes its basic setting (see section 2.3.3.8).
Connect the voltage to be measured via the BNC input socket. If required, an adapter with 4-mm sockets may be used.
The URE has a high-impedance input (10 MΩ shunted by < 40 pF). The external contact of the input socket is isolated from the earthed conductor (Fig. 2-1). The input capacitance is nearly frequency-independent. The input resistance decreases rapidly with increasing frequency as shown in Fig. 2-2. When measuring voltages of higher frequencies via a longer connecting cable, terminate the cable at the URE input so as to prevent measuring errors due to reflections.
Fig. 2-1 Equivalent diagram of the test input
Fig. 2-2 Input resistance
R 40830 - 2.6
The URE contains an overvoltage protection circuit. The following conditions must, however, at all times be fulfilled:
Fig. 2-3 Permissible input voltages
The AC, DC or AC+DC measurement mode is selected by pressing the appropriate key. The key lights to indicate the mode selected. Whenever one of the measurement mode keys is pressed, autoranging is switched on (the light of the RANGE HOLD key goes out) and V or mV is selected as display unit. The measurement speed selected is not affected and the state of the low-pass filter in the AC measuring section remains unchanged. In the DC measurement mode, all low-pass filter displays are switched off.
The URE measures the rms value of AC voltages from 50 µV to 300 V with crest factors up to 5. (The crest factor of AC voltages is defined as the ratio of the peak value to the rms value. With sinusoidal voltages it is √2.) The bandwidth is greater than 20 MHz but can be reduced to 100 kHz, 20 kHz or 4 kHz by means of the built-in low-pass filter (see section 2.3.3.5). The lower cut-off frequency is automatically set to 10 Hz, 100 Hz, or 1 kHz, respectively with the selection of the slow, fast or superfast measuring speed (see section 2.3.3.4).
To prevent interference voltages from entering into the test result, it is recommended - in particular with small test voltages - that the input signal be applied via a shielded cable and, if necessary, the low-pass filter be cut in. Make sure that the AC measuring circuit is not overdriven by excessive interference voltage when the low-pass filter is cut in.
In this case switch off the autoranging mode and select the appropriate range.
(see section 2.3.3.6)
The crest factor of AC voltages is in general limited to a maximum of 5. This limit is determined by the voltage range and the accuracy of the rectifier. It is possible to measure AC voltages with higher crest factors so long as the voltage range is not exceeded. The lower the rms value of the input voltage is relative to the selected measurement range, the higher is the permissible crest factor:
Permissible crest factor < 6 x Voltage range Rms value of voltage being measured .
For the manual setting of voltage range see section 2.3.3.6. The voltage ranges are given in Table 2-2.
The URE measures DC voltages in the range +300 V, with a resolution of 1 µV in the most sensitive measurement range. Superimposed AC voltages can be suppressed by means of a low-pass filter of a higher order which is switch-selected with the measurement speed (see section 2.3.3.4).
By simultaneously monitoring the input AC voltage a less sensitive measurement range is selected automatically if the limit values are exceeded.
The URE measures the rms value of the total input voltage. For this purpose, an AC measurement and a DC measurement are alternately carried out. The rms value of the total input voltage is then obtained by square-law addition of the two components. Voltage components whose frequencies are less than the lower cut-off frequency of the AC measuring circuit are not fully considered (see section 2.3.3.4).
The manifold calculation capabilities of the URE permit a test result to be displayed in the usual units V, mV, dBV or dBm or relative to a reference value. The associated keys V, dBV and dBm(Z) as well as AV, A%, AdB and V/REF are interactive and the selected indicating mode is illuminated on the front panel.
The numerical value is read out on a 4 1/2-digit 7-segment LED display. A positive sign is blanked. The result is not valid if the display blinks. Blinking may be caused by the measurement or indicating range being exceeded, as in the indicating mode A% or V/REF. If only the last digit blinks, the measured voltage is below the range of accurate measurement for the instrument voltage range cut in. A lower voltage range must then be switched in manually (see section 2.3.3.6).
When selecting the indicating mode V, the result - depending on the magnitude of the measured value - is read out in V or mV. The unit V or mV is also selected automatically when one of the measurement mode keys AC, DC or AC+DC has been pressed. A displayed dBV and dBm value ("Vm") is calculated as follows:
"Vm" dBV = 20 log Vm" dBv = 20 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 10 log Vm" dBn = 1
The resolution of the displayed dBV or dBm value is 0.01 dB. The maximum value indicated is +199.99 dBV/dBm.
A reference impedance Z of 0.0001 to 19999 Ω can be keyed in. The entered value is displayed when the RCL Z key is pressed. See sections 2.3.3.3 and 2.3.3.7.1.
In relative measurements, the result displayed is the measured value relative to a reference value. There are four possible indicating modes: difference between measured volts and reference volts (AV key), deviation from reference volts in % (A% key), logarithmic deviation (AdB key), and ratio of measured to reference volts (V/REF key). The reference voltage can be keyed in V, mV, dBV, or dBm. A display of the entered value is obtained by pressing the RCL REFA key. See section 2.3.3.3 and 2.3.3.7.1. It is also possible to use a measured value as a reference value.
The reference voltage is only required internally for calculating the indicated value. It can not be displayed unless it was entered as volts or mV. The various values displayed are given by the following equations:
Display Display Display
Example: V = 10 V; reference voltage = 20 dBm; reference impedance = 50 Ω. The URE calculates the reference voltage by use of the formula 20 dBm = 10 log VREF/50/1 mV to give VREF = 2.236 V. The above equations give the following indicated values: Display ΔV = 7.764 V; Display Δ% = 347.2%; Display ΔdB = 13.01 dB; Display V/REF = 4.472.
The resolution of measured values in the indicating modes A% and AdB is 0.01% and 0.01 dB respectively, with maximum indicated values +19999% and +199.99 dB. If the indicated value is > 199.99%, the resolution is lessened. The indicating range for the ratio of measured to reference voltage is 0.001 to 19999.
To identify relative readouts, the symbol \(\triangle \) lights up in addition to V, mV, % or dB as called for; when the ratio of measured to reference voltage is read out, only the symbol \(\Lefta\) lights up.
For quick detection of changes in the indicated value, a number of LEDs are arranged in a circle to provide a "tendency indication". The lighted LED corresponds to a particular indicated value. If the indication changes to a higher value, the light spot travels clockwise and if the indication drops to a lower value, the light spot travels counterclockwise. The tendency indication is also operative when the reference voltage or impedance is read out and when the keys are switched over to the second function. Thus the input voltage can be constantly monitored.
With AC and DC measurements the tendency indication is switched off.
When the RCL REFA is pressed, the stored reference voltage for relative measurements is displayed. When the RCL Z key is pressed, the reference impedance for dBm measurements is displayed. The selected key lights while all other keys go out. The reference voltage is displayed in the unit in which it was entered, i.e. in V, mV, dBV or dBm. During display of the reference voltage or reference impedance, the measuring section of the URE remains unchanged and autoranging and tendency indication remain active.
To reset the URE to the originally displayed measured value, the key involved, RCL REFA or RCL Z, is simply pressed again. It is also possible to obtain a new setting by pressing the function key AC, DC, or AC+DC, and key V, dBV, dBm(Z). AV. AG. AdB or V/REF.
SLCM (0.8/s), FAST (5/s) and SUPERFAST (50/s). Switchover from SLOW to FAST and vice versa is accomplished by means of the FAST key which lights when the FAST rate is selected. SUPERFAST can be selected with the aid of service function 3 (see section 2.3.3.7.2). The SUPERFAST setting is indicated by a light bar in front of the display. Because at SUPERFAST the measurement rate is slightly influenced by the selected output unit, output in volts must be set for maximum measurement speed.
is in volts. It can be selected with the aid of service function 3 (see section 2.3.3.7.2). The SUPERFAST setting is indicated by a light bar in front of the display.
The measurement rate is ganged with the filtering of the DC voltage which is applied to the A/D converter of the URE. The lower the selected measurement rate is, the lower are the cut-off frequencies of the two smoothing filters at the outputs of the AC and the DC measuring circuits. Hence, lowfrequency voltages can only be measured at a slow rate, and the DC measuring circuit suppresses AC voltages the more efficiently the lower the measurement rate selected. Fig. 2-4 shows the frequency characteristic of the DC measuring circuit as a function of the measurement rate.
Fig. 2-4 Frequency characteristic of the DC measuring circuit as a function of the measurement rate
In addition to the above-mentioned filtering of the rectified AC voltage, the lower cutoff frequency of the AC measuring circuit is selected together with the measurement rate. The 3-dB cut-off frequency is 10 Hz at the SLOW, 100 Hz at the FAST and 1 kHz at the SUPERFAST measurement speed. Fig. 2-5 shows the frequency characteristic of the AC measuring circuit as a function of the measurement rate. Switchover of the lower cutoff frequency offers the advantage that transients such as occur during range switching may be matched to the measurement rate.
Since the DC and the AC voltage components are measured alternately when carrying out AC+DC measurement, the same applies with respect to the influence of the measurement speed as has been said above.
Fig. 2-5 Frequency characteristic of the AC measuring circuit as a function of the measurement rate.
For suppression of unwanted frequencies when measuring AC or AC+DC voltages, the rectifier in the AC measuring circuit is preceded by a switchable lowpass filter which can be cut in and out by means of the LOWPASS key. With the filter cut in, three cut-off frequencies 4, 20 and 100 kHz are selectable (3-dB points) in the order 4 kHz, 20 kHz, 100 kHz, 4 kHz ... by pressing the SELECT key. The selected cut-off frequency and LP/kHz are illuminated and the LOWPASS key lighted. The cut-off frequency setting is not changed when the filter is switched in and out or the measuring mode is changed. When measuring DC voltage, the LOWPASS key and the cut-off frequency display are unlighted.
Since the low-pass filter used (2nd-order Butterworth filter) suppresses interference voltages very effectively, an interference voltage in the rejection region of the filter that is large in comparison with the voltage being measured can result in the URE input circuits being overdriven. As a rule of thumb, the components rejected by the filter should not be greater than the components passed. If they are greater, a larger voltage range must be selected manually (see section 2.3.3.6). Fig. 2-6 shows the frequency response of the switchable low-pass filter.
The URE is a voltmeter with autoranging, the switching speed of autoranging being matched to the measuremend speed. There are cases, however, where it is preferable to switch off autoranging and maintain a fixed voltage range. The RANGE HOLD key permits a voltage range selected by autoranging to be maintained. It is also possible to select any desired range with the use of service function 2 (see section 2.3.3.7.2). In both cases, the RANGE HOLD key lights. Automatic ranging can be switched back on by pressing the RANGE HOLD key again or by changing the measurement mode.
Holding an automatically selected voltage range is useful when the input voltage is switched off momentarily and switchover to the most sensitive range is to be avoided. Range selection with the use of service function 2 may be necessary to avoid overdriving of the amplifiers with the low-pass filter switched in. (See section 2.3.3.5 Switchable Low-pass Filter).
The measurement accuracy decreases very fast in the case of an undervoltage in the AC or DC measuring circuit. Therefore, the last digit of the display blinks when the measured AC voltage is less than 30% and the measured DC voltage is less than 10% below the nominal value. When this range is exceeded, i.e. when the measured value is more than 20% above the nominal upper limit of the range, or the AC-voltage proportion exceeds certain levels with DC measurements, the whole display blinks. The URE then changes over to the next higher voltage range. After the excessive voltage has been removed, the instrument returns to the original range. The voltage ranges are listed in Table 2-2.
With AC+DC measurement the AC and the DC circuits are tested separately for overvoltage and undervoltage. The range limits for both circuits are between 30% and 120% of the nominal upper limit of the voltage range.
The second functions of the keyboard - blue engravings on the keys - are used for entering data, such as the reference voltages for relative indications and the reference impedance for dBm measurements, as well as for calling up service functions, such as autocalibration. Switchover to the second functions is accomplished by means of the SHIFT key. This key lights when the second functions are selected; all other keys go out. The entire measuring circuit remains unchanged and the tendency indication and autoranging remain active. If the reference voltage or impedance is displayed at the time the second functions are switched in, the URE then automatically displays the last measured value.
For dBm measurements with the URE, a reference impedance must be entered and for relative measurements a reference voltage. For each of these quantities, a store is provided, whose contents are overwritten by a new entry. The store contents are not erased when the voltmeter is switched back on. The reference impedance is entered in ohms (Ω) and for the reference voltage V, mV, dBV or dBm can be chosen.
To enter a reference voltage or reference impedance, key in the appropriate number and unit, which are then displayed, and store the displayed entry by pressing the STO key. The URE automatically identifies an Ω entry as a reference impedance and a V, mV, dEV or dBm entry as a reference voltage.
R 40830 - 2.15
If the URE accepts the entry when the STO key is pressed, it automatically resumes its last setting. If an entry is illegal, the URE first displays the message
F--7
and then resumes the setting it had prior to the pressing of the STO key. Illegal entries are:
Reference voltage greater than +199.99 dBV/dBm Reference impedance negative or equal to zero.
For entry of the desired values, the second functions of the URE keys are used. These keys fall into two independent groups:
1) Numerical keys 0 to 9, decimal point key, +/- sign changeover key, CLEAR key
2) Unit keys, V/mV, dEV/dBm, Ω.
The entry of the numerical value with the keys of group 1 is performed in the same manner as with pocket calculators. The +/- sign can be changed during the entry as desired and a faulty entry can be corrected with the CLEAR key.
When pressing one of the unit keys, the first unit - V or dEV - is selected unless it has already been displayed. If the latter is true, the second unit - mV or dB - is selected. The unit can be changed during the entry as desired and is not influenced by the CLEAR key.
Example: Entry of reference value of 150.1 mV. Initially the URE is in normal operation, display in V. After entry of reference value, the URE is switched over to relative measurement - AdB.
Keys | Display |
---|---|
SHIFT | 3.002 V |
1 | 3.002 V |
- | 1. V |
5 | 15. V |
0 | 1122 |
150 . V | |
, | 150 . V |
1 | 150.1 V |
V/mV | 150 1 -17 |
STO | 190•1 mv |
AdB | 3.002 V |
26.02 dB |
As this example shows, the readout present prior to the switchover to the second function is preserved. It could be used immediately as the new reference value by storing it with the STO key. This is also the case if the URE was previously set for a relative measurement, but in this case, the volt-value corresponding to the readout would be stored with the STO key.
Example: Entry of the last value measured as reference value. Initially the URE is in normal operation, display in V. Then it is switched over to relative measurements - △% -. After entry- display of reference value.
Keys | Display |
---|---|
14.14 V | |
RCL REFA | 14.392 V |
∆% | |
SHIET | -1.75 % |
SHIT I | -1.75 % |
STO | |
BCI. REFA | 0.00 % |
14.14 V |
The service functions of the URE are special device functions. They are only rarely required so that no particular key is provided for them. They are called up by pressing the SHIFT key to activate the second functions of the URE keys and then pressing the decimal point key "." three times in succession. The readout on the display is then
and after entry of the required code, as given in Table 2-1, the selected function is executed. After execution of functions 0 to 4, the URE resumes its last setting.
Table 2-1 Service functions
Code | Function | |||
---|---|---|---|---|
ø | Display test | |||
1 | Display of IEC-bus address | |||
2 | Selection of voltage range | |||
3 | Measurement speed SUPERFAST | |||
4 | Autocalibration | see | section | 3.3.1 |
5 | Absolute value adjustment | 11 | Ħ | 5.2.1.1 |
6 | Rectifier adjustment | n | 11 | 5.2.1.1 |
7 | Analog output - offset adjustment | п | u | 5.2.1.1 |
8 | Analog output - amplifier adjustment | 11 | 11 | 5.2.1.1 |
9 | Reference voltage adjustment | н | 11 | 5.2.1.1 |
Example: Display of IEC-bus address
Keys | Display |
---|---|
SHIER | XXXXXX |
Shirt I | XXXXXX |
• | 0. |
• | 0. |
• | - SEr - |
Ţ | IEC 7 |
XXXXX |
Service function 0 - display check - causes all indicating elements including the illuminated keys to light for about 3 s.
Service function 3 permits the measurement speed SUPERFAST to be selected. After this, the FAST key lights up and in the left corner of the display an illuminated bar appears. By pressing the FAST key, the URE is reset to FAST measurement speed.
The service function 4 is dealt with in section 3.3.1.
The service functions 5 to 9 are dealt with in section 5.2.1.1.
Only service function 2 - selection of voltage range - will be discussed here.
After pressing the code number 2 for this service function, the desired range number, given in Table 2-2, is entered and the instrument goes over into this measurement range. After resetting to measured value display, the RANGE HOLD key lights. Since the DC measurement circuit, owing to its enhanced dynamic characteristics, permits the voltage ranges to be graduated in 20-dB steps, only those ranges that are not marked with an asterisk in Table 2-2 can be selected for measuring DC voltages. If another range is selected, the URE automatically switches over to the next higher DC range. Note that prior to setting the voltage range, the measurement mode - AC, DC or AC+DC - must be selected.
Table 2-2 Range numbers for service function 2
lange number | Measurement range |
---|---|
01 | 1 mV +) |
02 | 3 mV +) |
03 | 10 mV |
04 | 30 mV +) |
05 | 100 mV |
06 | 300 mV +) |
07 | 1 🗸 |
08 | 3 v +) |
09 | 10 V |
10 | 30 v +) |
11 | 100 V |
12 | 300 V |
+) Only possible for measuring AC and AC+DC voltages.
Example: Setting of measurement range 1 V
Keys | Display |
---|---|
OUTON | xxxxx |
SHIFT | xxxxxx |
• | 0. |
• | 0. |
٠ | SEX |
2 | - 357 - |
0 | 2 |
7 | 20 |
• | 2 07 |
XXXXX |
The basic setting of the URE is automatically activated when the instrument is switched on. This setting is also switched in via IEC-bus control with the commands CL or DCL (Device Clear) or SDC (Selected Device Clear) (see sections 2.3.4.3.1 and 2.3.4.5.2).
The basic setting is as follows:
Measurement mode | AC |
---|---|
Output of measured voltage in | V |
Measurement speed | FAST |
Low-pass filter | OFF |
RANGE HOLD | OFF |
Furthermore, the IEC-bus interface is set to the delimiter CR+NL (Carriage Return and New Line) for data output (W3), and no Service Request is sent (QØ). Alphanumeric data output (NØ) via IEC bus, and the URE operates without the measuring time being reduced (VØ).
The basic setting corresponds to the following sequence of IEC-bus instructions
RAØ, UØ, F1, LØ, W3, QØ, NØ, VØ.
The reference voltage and the reference impedance are not affected by the basic setting.
The display
1-,-,-
followed by a hexadecimal 1...F indicates that the URE is not functioning properly. The errors causing this display are described in section 5.2.1.2. By pressing a DISPLAY key, the error message display is erased and data display selected. If the error occurs again, the error message is again displayed.
Regarding the display
[-,-,-]]
see section 2.3.3.7.1.
When displaying the reference values (key RCL Z or RCL REF A) or when changing over to the second functions (key SHIFT) the error message remains erased, and appears again only when switching over to data display.
The UFE may be fitted with a remote-control interface in accordance with IEC Publ. 625-1 for connecting it into an IEC-bus system for transfer of setting and measurement data. This permits all functions of the URE to be remote-controlled. The IEC-bus connector 20 (Fig. 2-7) is located on the rear panel of the URE. For retrofitting the IEC-bus option see section 2.3.4.
The interface characteristics of the IEC bus (control lines, handshake lines, data lines) as well as the data transfer sequence are laid down in the relevant standards. The ASCII characters used for data transfer are listed in Table 2-15.
Fig. 2-7
The address switch (coding switches A1 to A5) provides for setting the device address in binary code. Table 2-14 shows the relationship between device address, switch positions, and ASCII characters for listener and talker address. the URE is factory-set to device address 7.
The Talk Only mode (see section 2.3.4.6) is also set by means of the address switch with the extreme right coding switch in TALK ONLY position.
The setting of the address switch is read in at switch-on and by calling up service function 1 (display of IEC-bus address) and read out on the display (see section 2.2.4).
The URE implements the following interface functions:
SH1 | Source handshake function, |
---|---|
complete capability | |
AH1 | Acceptor handshake function, complete capability |
Т5 |
Talker function, capability to answer serial poll,
unaddressing if MLA, Talk Only mode |
L4 | Listener function, unaddressing if MTA |
SR1 |
Service Request,
complete capability |
RL1 | Remote/local switchover function, complete capability |
DC1 |
Device Clear function,
complete capability |
DT1 | Device Trigger function, |
These instructions can be subdivided into five groups:
5) Service instructions (Table 2-9)
Required for necessary adjustments or repair of the device (see sections 3..., 4..., 5...).
The service instructions are of the same type as the setting and device trigger instructions.
All IEC-bus device instructions consist of an alphanumeric header, the numeric content, a separator, which separates several instructions from each other, and delimiters which terminate a sequence of instructions (Table 2-3). The header consists of one or two ASCII upper-case letters and a numeric part of, in general, one or two digits. The numeric content may in addition to numbers include decimal point, sign, and the upper-case letter E, for exponent. Any of the delimiters may be used. Spaces may be used in the instruction sequence.
Example of instruction sequence (Controller PUC): IECOUT7. "instruction 1, instruction 2, instruction 3" /CR/NL/
All the instructions received are checked for correct syntax, and all the data received are checked to see that they are within the limit values. If errors are found, these instructions are not executed and instead - after the interface is set as required (Table 2-7) - a Service Request with appropriate status-byte coding (Table 2-13) is generated.
Cl activates the basic setting of the URE (see section 2.3.3.8 Basic Setting) and corresponds to the following sequence of instructions
RAØ, UØ, F1, LØ, W3, QØ, NØ, VØ. With the instructions FØ to F2 the measurement speed of the URE is set (see section 2.3.3.4 Measurement Speed).
With the instructions L1 to L2 the low-pass filter in the AC circuit is set to the required limit frequency and is cut off again with instruction LØ (see section 2.3.3.5 Switchable Low-pass Filter).
With setting NØ in data output the numerical value is preceded by an alphanumeric header of six characters (see section 2.3.4.4). The header can be suppressed with instruction N1.
Instructions UØ to U6 determine the output unit (see sections 2.3.3.2.1, 2.3.3.2.2 and 2.3.4.4).
The instructions VØ to V2 allow for a compensation of the time delay between the measurement voltage and the trigger instruction making thus optimum use of the short measuring time in the SUPERFAST mode.
The URE receives together with the voltage to be measured a trigger instruction. After the elapse of measurement time TM, the measurement value can be read off from the output buffer.
If with respect to the voltage to be measured, the trigger instruction arrives with a delay of 10 ms on the URE, the measurement value would be available at the output buffer only after TM plus 10 ms.
With the instruction V2 the delay of 10 ms could be taken into account so that for the above example the measurement value would also be available after TM as referred to the measurement voltage. The accuracy of the result will not be affected as long as the compensation time selected remains below the actual delay time.
The instruction VØ, VI or V2 remains active until change over.
With instruction V? the selected compensation time can be read out.
With the Interface Q1 set correspondingly, the URE communicates Service Request after receiving instruction V?. By decoding the status byte the compensation time can be read out (see section 2.3.4.5.4. Service Request).
With the instructions RA/range number/, RD/range number/ and RC/range number, the function and voltage range are always set together. In contrast to key control, the output unit is not affected when the function is changed. Since the DC measuring circuit with its greater dynamic range permits division of the measurement ranges in 20-dB steps, only the ranges not marked with an asterisk in Table 2-5 can be set when measuring DC voltage. If an unpermitted range is selected, the URE automatically switches to the next higher measurement range. Thus, for example, the instructions
RD1, RD2 and RD3
all have the same effect - they set the 10-mV range.
The data can be entered with or without exponent. The exponent may consist of two digits maximum and the (+/-) sign. The length of the mantissa can be freely chosen. However, only so many characters are accepted as could be entered in the display by hand (see section 2.3.3.7.1). A positive sign or a zero before the decimal point can be entered or not. Spaces do not affect the entry.
Example: Entry of a reference value of 0.316 V. The following instructions are all equivalent: DVO/.316, DV.316, DV+Ø.316, DV Ø.316, DV316E-3.
The delimiter of the data output is set by means of WØ,...,W8. Status-byte coding in the case of a Service Request is described in section 2.3.4.5.4 (Table 2-13).
Like the universal instruction GET (see section 2.3.4.5.3), the trigger instruction XI causes the URE to start a measurement at the selected settings and store the result in the output buffer. With the interface set appropriately, a Service Request is sent at the end of the measurement.
The instruction X2 has the same effect as X1 or GET with the difference that the measured value is used as reference value.
Two special features of X2 should in addition be high-lighted:
If one of the relative units (control character U3...U6) is selected for the output unit, the measured value obtained by instruction X2 is expressed relative to the original reference value. The reference value produced by X2 is used for the evaluation of measured values only after subsequent triggering. This is due to the following measurement cycle of the URE:
4. Storing measured value as (new) reference value
If the control character X2 is used, it should always be sent before the terminator since the URE is inhibited for further commands on the reception of X2. In other words, with setting commands sent after X2 the IEC bus remains
blocked until X2 is processed (i.e. 1.2 s for SLOW speed of measurement).
The instruction X5 is not an inhibiting instruction in the real sense, but it sets the URE so that a command for measurement from the controller initiates triggering.
Example (PPC):
IECOUT7, "X3"
(setting up trigger logic)
IECIN7, AS (triggering and read in of measured value for variable AS)
The instruction X3 offers the advantage of doing away with the special trigger instruction (X1, X2, GET) which brings about a higher speed of measurement.
Like X3 the instruction X4 is a setting instruction and performs sequence measurements, i.e. the URE starts a measurement by itself and continues with the next provided that the previous measurement is completed. This enables to attain the highest possible speed of measurement.
The settings of X3 and X4 can be reset with the control character XØ.
The instructions ZØ and Z1 cause the URE to store the reference voltage or reference impedance in the output buffer.
The instructions SA, ..., SP permit device calibration data and error numbers to be stored in the output buffer (see section 5.2.1.2). By talker address, the output buffer can be read out, but only once. No instruction may be sent between the trigger instructions and talker address. The output data format is described in section 2.3.4.4.
These instructions serve the same purpose as their corresponding service functions. For more details see sections 3.3.1 and 5.2.1.1.
Since autocalibration of the URE takes several seconds, the service instruction S4 should only be sent alone or at the end of an instruction sequence. This prevents the IEC bus from being blocked while the instruction is being executed.
Symbol | Name | ASCII decimal equivalent | Application |
---|---|---|---|
, | Komma. | 44 |
Separator between
individual instructions |
CR
NL ETX |
Carriage Return
New Line |
13
10 3 |
Delimiters |
Instruction code | Function | |
---|---|---|
C1 · | Basic setting | |
F0
F1 F2 |
SLOW
FAST SUPERFAST |
Measurement speed |
LO
L1 L2 L3 |
OFF
4 kHz 20 kHz 100 kHz |
Low-pass filter |
NØ
N1 |
Output with
Output without |
Alphanumeric header |
UO
U1 U2 U3 U4 U5 U6 |
V
dBV dBm AV A% AdB V/REF |
Output unit |
VØ
V1 V2 |
Øms
5ms 10ms |
Compensation time with
trigger delay |
Λ. |
Request for compen-
sation time |
(Service request with correspondingly set status byte) |
RA/range numbe
RD/range numbe RC/range numbe |
er/ AC
er/ DC er/ AC+DC |
Function + voltage range. |
Measurement range |
---|
Autoranging, |
1 mV |
3 mV +) |
10 mV. |
30 mV + |
100 mV |
300 mV + |
1 V. |
3 V +) |
10 V. |
30 V + ) |
100 V |
300 V |
Table 2-5 Setting instructions - range numbers
+) Only when measuring AC or AC+DC
Table 2-6 Data entry instructions
Instruction code | Function |
---|---|
DV/data/ | Reference voltage in V |
DB/data/ | Reference voltage in dBV |
DM/data/ | Reference voltage in dBm |
DZ/data/ | Reference impedance in ohms (Ω) |
Table 2-7 Interface instructions
Instructi | on code | Function |
---|---|---|
WO
W1 W2 W3 W4 W5 |
NL
CR ETX CR+NL EOI NL+EOI |
Delimiters |
W6
W7 W8 |
CR+EOI
ETX+EOI CR+NL+EOI |
|
ର୍ଠ
ରୁ1 |
No SRQ
SRQ |
|
H1 | (see section | 2.3.4.5.5) |
Function | |
---|---|
хø | Reset function for instruction |
xı |
X3 and X4
Trigger instruction = GET |
X2
X3 |
Trigger instruction plus transferring
measurement value as reference value Setting instruction for triggering with |
x4 |
request for measurement
Setting instruction for sequence of |
_____
Instruction code | Function |
---|---|
S0
S1 S2 S3 S4 S5 S6 S7 S8 |
Display check
Reference voltage adjustment 100 mV Reference voltage adjustment 1 V Reference voltage adjustment 10 V Autocalibration Absolute value adjustment Rectifier adjustment Analog output - offset adjustment Analog output - gain adjustment |
SA
SB SC SD SE SF SG SH SI SJ SX SL SM SN |
1
2 3 4 5 6 Display of calibration data 7 of measurement range 8 9 10 11 12 13 14 |
SO | Display of linearity coefficient of rectifier |
SP | Display of error number |
The URE can output the measured data, the reference voltage, the reference impedance, the error number, and the device calibration data. The output format is the same for the Talk Only mode and the talker status after having been addressed by the controller. The output may either be a numerical value (control character N1) or a numerical value with a preceding six character alphanumeric header (control character NØ). The numerical value is preceded by a total of six characters (Fig. 2-8), namely two characters for the measuring function (Table 2-10, three characters for the unit (Table 2-11), and one character for identifying the output data when the measurement range is exceeded or the reference value is output, etc., (Table 2-12). The code H is displayed not only for overrange but also when autoranging of the URE is stopped after several unsuccessful search of range.
Fig. 2-8 Data output format
Code
The numerical value is generally not output with exponent. The exponent E-3 is added only if mV is displayed.
Example: Output of valid measured data 177.3 mV (DC) DCV---177.3 E-3 Output of measured data 12.17 dBm (AC) if below range limit ACDEMU12.17 Output of reference value 9.502 V --V--R9.502
The data output is terminated by the set delimiter (Table 2-7).
Table 2-10 Coding of measuring function for data output
Measuring lunction | |
---|---|
AC | AC |
DC | DC · Space |
CC | AC+DC Space |
Cutput of reference voltage, reference impedance
or calibration value |
Code | Output unit | ||
---|---|---|---|
V
DBV DEM DV- D%- DDB REL |
V
dBV dBm △V △% △dB V/REF |
_: Space | |
with calibration value |
Table 2-12 Identification of output data
code | Function |
---|---|
-
н |
Valid measured data
Above range limit |
0 | Overflow of readout : Space |
R | Reference voltage/Reference impedance /Calibration valu |
U | Below range limit |
If the URE receives its listener address from a controller, it will switch over to the remote state in accordance with the standard and remain in this state even after completion of the data transfer. All the operating controls on the front panel are disabled in the remote state but displays and the illumination of the keys remain operative. The analog output also remains operative. The remote state is indicated by REM and by
LIS (URE addressed as a listener), TAL (URE addressed as a talker), or SRQ (URE sends Service Request)
lighting up. This permits the state of the interface function to be checked, which is particularly useful for testing purposes. If the instruction GTL (Go to Local) is received, or if the LOCAL key is pressed, the URE switches to the local state and can then be set manually.
The indication REM disappears; LIS and TAL remain operative.
If the key LOCAL is not inhibited (see below), it has priority over the IEC bus. This means that a transfer to the bus can be interrupted by LOCAL. With the URE in TALK mode, activating the key LOCAL before sending the delimiter
can even block the IEC bus. The key LOCAL can be blocked by the controller with the command LLO (Local Lockout).
For the change of status remote - local - remote the settings QØ, Q1 NØ, N1 WØ ... W8 VØ ... V2 are retained.
If the controller sends the universal instruction DCL (Device Clear) or the addressed instruction SDC (Selected Device Clear), the URE assumes its basic setting (see section 2.3.3.8). The basic setting is also activated on switch-on of the URE or if the IEC-bus instruction Cl is issued.
On receiving the addressed instruction GET (Group Execute Trigger), the URE starts immediately a measurement at the selected setting. This trigger instruction corresponds to the device trigger instruction X1 (see section 2.3.4.3.4).
Setting the SRQ (Service Request) line enables the URE to request service from the controller. This proves useful when the end of a measurement, an autocalibration, or a fault is to be communicated to the controller. The instructions QØ and Q1 (Table 2-7) permit the interface to be set accordingly.
If the controller executes a Serial Poll after having received a Service Request, it can determine the device status that caused the issue of the Service Request by decoding the status byte (Fig. 2-9 and Table 2-13).
Fig. 2-9 Status byte
Device status | Status byte | Decimal equivalent |
---|---|---|
End of measurement | LHLHLLLL | 80 |
End of autocalibration without error | LHLHLLH | 81 |
Compensation time
Øms 5 ms 10 ms |
82
83 84 |
|
End of autocalibration with error | LHHHLLLH | 113 |
Syntax error in
IEC-bus instruction |
LHH,LLLL | 96 |
Incorrect input data | LHHLLLHL | 98 |
Talker address without previous trigger | LHHLLLHH | 99 |
Improper function of hardware | LHHLLHLL | 100 |
Since the CEM computer processes INPUT commands asynchronously after 64 ms (version 82), errors may well occur in the data transfer from URE to the controller. If the URE is transferring the 1St character while the computer stops the. INPUT, the URE continues with the second character for the next TALK address so that the string read in to the computer does not contain the first character. For this reason, the URE can be programmed with the instruction HI such that the transfer begins with the first character on TALK addressing. The instruction HI should only be applied to the CEM computer so that transfer of part of a string remains possible for other controllers. HI can be made inactive using the instructions
C1 (Basic setting) DCL (Device clear) SDC (Selected device clear)
as well as by switching off and on the URE.
When using CEM computers (version 1982) it should also be noted that the URE uses delimiter CR (instruction W1).
Table 2-14 Setting the device address
Abolt character | Binary address | Desimal |
---|---|---|
Listener Talker
address address |
Address switch
A5 A4 A3 A2 A1 |
equivalent |
(SPACE) (a)
! A B C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D # C D P Q R S T U V W X Y Z [ ] C D = C D # C D N C D P Q R S T U V W X Y Z [ ] C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C D = C C D = C C C C C C C C C C C C C |
L
L H L H L H H L H H L L H H L L H L L L H H L L H H L L H H L L H H L L H H L H H L H H L H H L H H L H H L H H L H H L H H L H H L H H L H H L H H H H |
0
1 2 3 4 5 6 +) 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 |
+) Factory-set
by 60 | 000 | MSG | °°, | MSG | 0,0 | MSG |
- 0 |
MSG | 00, | MSG | • | MSG | MSG | MSG | ||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
-7- | 4 | 1 | - | COLUMN | 0 | - | 2 | 3 | 4 | S | $ | 7 | ||||||||
0 | 0 | 0 0 | 0 | 0 | NUL | DLE | SP | - | 0 | - | ۲ | - | ٩ | F | ŀ | - | • | F | ||
0 | 0 | - | - | SOH | GTL | DCI | 1L0 | - | - | < | F | ٩ | • | ٩ | - | |||||
0 | - 0 | 0 | 2 | STX | DC2 | - | 2 | 8 | æ | م | - | F | ||||||||
0 | - 0 | 1 | m | ETX | DC3 | Ħ | 3 | υ | s | υ | DDE | 8 | ||||||||
0 | 0 | 0 | 4 | EOT | SDC | DC4 | DCL | ~ | - | 4 | ٥ | н | - | Р | - |
|
))) |
||||
0 | 0 | - | 5 | ENQ | DPdd | NAK | РРU | ж | зэл | 5 | I CE | ш |
|
301 |
n |
|
| | | |
• | 90a | 2 | 90a | |
0 | - | 0 | 9 | ACK | SYN | 2 | EV | 6 | E۸ | ш | EV | > |
|
| | |
- | > | |||||
0 | - | - | ۲ | BEL | ETB | ٠ | ac | 1 | ac | ა | ao | B |
a o
l |
8 ( | 3 | 80 | ||||
- | 0 | 0 | 8 | BS | GET | CAN | SPE | - | 8 | I | × |
)
T |
4 | NEL | × | NET | ||||
- | 0 0 | - | 9 | HT | TCT | EM | SPD | - | NED | 6 |
|
1ED |
- |
|
| | |
۲ |
|
| | |
- | 133 | ۲ | 193 | |
- | - 0 | 0 | 10 | NL | SUB | * | 10 | 191 | - | 191 | Z |
|
|91 |
- | DE | z | D | ||||
- | - 0 | - | п | ٧T | ESC | + |
|
551 |
•• | ssi | × | ss | - | ss. | × | NG | - |
|
9N | |
|||
- | 0 1 | 0 | 12 | FF | FS | • | v v | * |
₹ ∀
| |
L |
4 4
| |
- |
4 A
| | |
- | INA | I NA | ||||
- | 0 1 | - | 13 | СК | GS | 1 | าพ | 1 |
|
| | |
¥ | TM | - | TM | ε | WE | - | WE' | |||
- | = | 0 | 14 | 50 | RS | ^ | • | z | ¢ | - | c | 2 | ||||||||
- | = | - | 15 | SI | λ | ` | + | ċ | UNL | 0 | 1 | 0 | • | DEL | ||||||
K | ſ | L | ] § | L | 6 | ſ | L | _ | ||||||||||||
COP | RESSED | COMP | AND | Ð | ADDI |
STEN
RESS |
ADI |
LK
DRESS |
/ | |||||||||||
(00P | (UC | L GR | 46) |
CR
(T) |
46) | / | / | / | ||||||||||||
J | P | ٦ | ر | ٦ | ||||||||||||||||
РВ | IMARY | COMMAN | D GROU | P (PCG | ~ | SECO | VDARY | |||||||||||||
COMI | JAND | |||||||||||||||||||
ON | TES | :: | M | 56 = | INTERF. | ACE MES | SAGE | ы | (SC | |||||||||||
2) b | 1 = D | 101 | b, = DI | 07 | i | |||||||||||||||
0 | B R | EQUIRI | ES SEC | ONDARY | COMMAN | Q | ||||||||||||||
0 | D D | ENSE | SUBSET | (colum | IN 2 TH | ROUGH | 5) |
(SENT AND RECEIVED WITH ATN=1)
R 40830 - 2.36
Table 2-15
For the printout of measurement data without an IEC-bus controller, the data can be output via the IEC-bus connector to a Listen Only device having an IEC-625 interface. For this, the device used, for example a printer, is set to LISTEN ONLY and the URE to TALK ONLY (see section 2.3.4.1).
In this operating mode, the URE is operated from the front panel and any of the data displayed can be output to the Listen Only device by pressing the LOCAL key. The coding is described in section 2.3.4.4. The delimiter setting is fixed, each output being terminated by CR + NL (Carriage Return + New Line).
The IEC-bus option retrofitting kit consists of the following items (see Figs. 2+11 and 2-12):
For mounting the IEC-bus option, refer to Figs. 2-11 and 2-12. Performance checking is described in section 3....
- Insert the light bar module 10 into the socket provided for this purpose. The mounting position is irrelevant but make sure that the module is flush with the display window.
The Analog Output Option permits a DC voltage proportional to the indicated value to be output. This voltage is produced by means of a 12-bit D/A converter at the display rate, i.e. when the URE is operated via the IEC bus the voltage value can only be renewed by initiating a measurement. The operating range of the output voltage is -2 to +2 V with a resolution of 1 mV (Zout = 100 Ω). The output is referred to the earth conductor, not to the outer contact of the input socket.
The relationship between the output voltage and the display is given by the following equation:
Output voltage | - | Displayed value without decimal poir | ıt |
---|---|---|---|
V | 10 000 |
Example:
Display | Output voltage |
---|---|
11.500 V | +1.150 V |
-37.25 dBV | -0.372 V |
1.13% | +0.011 V |
When changing over to the second key function or when the reference voltage and reference impedance are displayed, there is still a voltage output corresponding to the measured value.
The fact that the output voltage is related to the displayed value and not to the measured voltage offers interesting possibilities:
Lin. | output, | absolute | (V) | |
---|---|---|---|---|
Lin. | output, | normalized | (V/REF, 4%) | |
Lin. | output, | with/without | offset | (∆V, ∆%) |
Log. | output | (dBV, dBm) | ||
Log. | output, | with/without | offset | (∆dB). |
It should be borne in mind that output voltage jumps may be caused if the number of display digits is changed due to range switching or change of display format. Range switching caused by voltages below the range limit
can be avoided by means of the RANGE HOLD key or by direct setting by means of service function 2 (see section 2.3.3.6). However, if the test voltage changes are considerable, the display should be switched over to dBV, dBm, \[\Delta dB or \Delta \%. In the logarithmic display mode, the resolution is always 0.01 dB, i.e. the output voltage changes by 10 mV if the measured value changes by 1 dB. The indicating range from -199.99 to +199.99 (dBV, dBm, \Delta dB) covers the entire measurement range of the URE. In the indicating mode \Delta, the resolution is constant within the range from -199.99 to +199.99% and is 0.01%, so that the output voltage over this range changes by 10 mV if the measured value changes by 1%.
The analog output option retrofitting kit consists of the following items (see Fig. 2.13):
1 ea DC output board 9
1 ea connecting cable 10
2 ea socket including accessories 1, 2, 3, 4, 5, 6.
For mounting the analog output option, refer to Fig. 2-13. Readjustment of the voltmeter is not required. For performance checking see section 3....
3. Maintenance
See Table 3-16 in Appendix.
RMS Voltmeter URE is specified for operation in the temperature range +5° to +45°C (IEC-359 Applications Class 1).
The tolerances for the measured values given in this section apply to the limited temperature range +15° to +30°C as laid down in section 1 of URE Data Sheet.
The test procedures of this section apply for the entire operating temperature range of the URE and may be used, if necessary, with the extended tolerances given in the Data Sheet.
The AC supply voltage must lie within +10% of the nominal value to which the instrument has been set (section 2.2.3).
Except when otherwise specified, the instrument settings are made manually (i.e. not by means of an IEC-bus controller).
To check the nominal values of the URE a minimum warm-up time of 30 minutes must be allowed for.
When service function 0 is called (section 2.3.3.7.2), all indications, including the key illumination, must light (Fig. 2-9). The return to the measurement mode occurs automatically after 3 seconds.
The illuminated display for remote status is included in the URE only when the IEC-bus option is built-in.
The proper functioning of all keys must be checked. Initial URE settings: SHIFT key not activated
Key Input | Function | Indication |
---|---|---|
AC | AC measurement | AC key lights |
DC | DC measurement | DC key lights |
AC+DC | AC+DC measurement | AC+DC key lights |
RCL Z |
Display of stored
reference impedance |
RCL Z key lights, other
key illumination is off |
RCL REF |
Display of stored
reference voltage |
RCL REFA key lights, other key illumination is off |
RANGE HOLD |
Automatic range
selection disabled |
RANGE HOLD key lights |
FAST f>100 Hz | Switch-over of measuring speed | FAST key lights |
LOW PASS |
Measuring bandwidth
limited |
LOW PASS key lights,
LP/kHz display lights |
SELECT |
Switch-in of low-
pass cutoff frequency |
Illuminated display:
4 -> 20 or 20 -> 100 or 100 -> 4 |
dBV | dBV indication | dBV in display area lights |
dBm (Z) | dBm indication | dBm in display area lights |
v | Voltage indication |
mV or V in display area
lights |
2 V | Relative voltage indication |
mV or V and △ in display
area light |
2% | % indication | % and △ in display area light |
1dB | dB indication |
dB and ∆ in display area
light |
I/REF | Relative indication | △ in display area lights |
SHIFT | Switch-over to the second functions | SHIFT key lights, other key illumination is off |
STO |
Storage of reference
voltage and impedance, return to measuring function |
SHIFT key illumination
switched off |
The test setups are shown in Figs. 3-1. 3-2 and 3-3 at end of this section.
URE settings:
Operating mode: AC
Display mode: V
Filters: LOW PASS out. SLOW (FAST out)
Procedure A, For measured voltages > 30 mV, setup of Fig. 3-1:
- Adjust AC voltage and frequency at the AC calibrator and apply to URE test terminal.
- Check the URE indicated values according to Table 3-1.
Procedure B, For measured voltages < 30 mV, setup of Fig. 3-2:
Mahla | 7 1 |
Table | 7-1 |
- |
URE range
selection |
Test volt
and frequ |
age
lency |
URE measu-
rement range |
URE indi
Nominal value |
cation
| Permitted | deviation |
---|---|---|---|---|---|
Automatic
(RANGE HOLD off) |
Set on
AC calibr 80 mV |
10 Hz
100 Hz 1 kHz 10 kHz 100 kHz |
100 mV |
80.00 mV
80.00 mV 80.00 mV 80.00 mV 80.00 mV 80.00 mV |
+2%
+0.5% +0.5% +0.5% +0.5% |
RANGE HOLD |
80 mV
100 mV |
100 kHz
10 kHz |
100 mV
100 mV |
100.00 mV | +0.5% +) |
Automatic |
200 mV
316.2 mV 800 mV |
10 kHz
10 kHz 100 Hz 1 kHz 10 kHz 100 kHz |
300 mV
300 mV 1 V |
200.0 mV
316.2 mV .8000 V .8000 V .8000 V .8000 V |
+0.5% +)
+0.5% +) +0.5% +0.5% +0.5% +0.5% |
RANGE HOLD |
800 mV
1 V |
100 kHz
10 kHz |
1 V
1 V |
1.0000 V | + 0.5% +) |
Automatic | 2 V | 10 kHz | 3 V | 2.000 V | +0.5% |
RANGE HOLD |
2 V
3.162 V |
10 kHz
10 kHz |
3 V
3 V |
3.162 V | + 0.5% |
Automatic | 8 V | 10 kHz | 10 V | 8.000 V | + 0.5% |
RANGE HOLD |
8 V
10 V |
10 kHz
10 kHz |
10 V
10 V |
10.000 V | + 0.5% |
Automatic |
20 V
80 V 300 V |
10 kHz
100 Hz 1 kHz 10 kHz 100 kHz 20 kHz |
30 V
100 V 300 V |
20.00 V
80.00 V 80.00 V 80.00 V 80.00 V 300.0 V |
+0.5%
+0.5% +0.5% +0.5% +0.5% +0.5% |
+) The indicated voltage serves as reference value for wideband voltage measurements up to 20 MHz in the particular measurement range.
URE range
selection |
Test voltage and
frequency |
URE measu-
rement range |
URE ind
Nominal value |
|
ication | Permitted | deviation |
|
---|---|---|---|---|---|
Automatic |
Set on signal
generator 80 mV 10 kHz |
Attenu-
ator box setting 20 dB |
100 mV | ||
RANGE HOLD |
I
100 mV 10 kHz Adjust to refer previous calibr |
20 dB
rence value ration (see |
100 mV
obtained in note under 1 |
100.00 mV
Cable 3-1) |
+ 0.5% |
Automatic |
0.1 mV 10 kl
0.3162 mV 10 kl 1 mV 10 kl 3.162 mV 10 kl 10 mV 10 kl 31.62 mV 10 kl |
Hz 80 dB
Hz 70 dB Hz 60 dB Hz 50 dB Hz 40 dB Hz 30 dB |
1 mV
1 mV 1 mV 3 mV 10 mV 30 mV |
.100 mV
.316 mV 1.000 mV 3.162 mV 10.000 mV 31.62 mV |
+(0.5% +15 μV)
+(0.5% +4 μV) +(0.5% +1 μV) +0.5% +0.5% +0.5% |
URE settings: Operating mode: AC Display mode: V Filters: LOW PASS out, SLOW in (= FAST out) Measurement range: Set by use of service function 2 (section 2.3.3.7.2) with entry of range number as given in Table 3-3. Test Procedure A, For measured voltages ≤ 1 V Use setup of Fig. 3-2.
Test Procedure B, For measured voltages from 1 V to 10 V Use setup of Fig. 3-3.
URE range
number setting |
Test voltage
and frequency |
URE measu-
rement range |
URE inc
Nominal value |
lication
Permitted deviation |
|
---|---|---|---|---|---|
Signal genera-
tor setting |
Attenua-
tor setting |
||||
05 | 100 mV 10 kHz | 20 dB | 100 mV | 100.00 mV | +0.5% |
Adjust URE indica
calibration. |
tion to rep | ference value | e obtained | in | |
100 mV 200 kHz
1 MHz 3 MHz 10 MHz 20 MHz |
20 dB | 100 mV |
100.00 mV
100.00 mV 100.00 mV 100.00 mV 100.00 mV |
+0.7%
+0.7% +1.5% +4% +10% typ. |
|
04 |
31.62 mV 10 kHz
10 MHz |
30 dB | 30 mV |
31.62 mV
31.62 mV |
+0.5%
+4% |
03 |
10 mV 10 kHz
10 MHz |
40 dB | 10 mV |
10.000 mV
10.000 mV |
+0.5%
+4% |
02 |
3.162 mV 10 kHz
200 kHz 1 MHz 3 MHz 20 MHz |
50 dB |
3 mV
3 mV |
3.162 mV
3.162 mV 3.162 mV 3.162 mV 3.162 mV 3.162 mV |
+0.5%
+0.7% +0.7% +3% +15% typ. |
01 |
1 mV 10 kHz
10 MHz |
1 mV |
1.000 mV
1.000 mV |
+(0.5% +1 μV)
|
|
06 | 316.2 mV 10 kHz | 10 dB | 300 mV | 316.2 mV | +0.5% |
Adjust URE indicat calibration. | ion to ref | erence value | obtained | in | |
316.2 mV 10 MHz | 10 dB | 300 mV | 316.2 mV | + 4% | |
07 | 1 V 10 kHz | 0 dB | l V | 1.0000 V | ±0.5% |
Adjust URE indicat calibration. | ion to ref | erence value | obtained : | in | |
1 V 200 kHz
1 MHz 3 MHz 10 MHz 20 MHz |
0 dB | 1 V |
1.0000 V
1.0000 V 1.0000 V 1.0000 V 1.0000 V |
+0.7%
+0.7% +1.5% +4% +10% typ. |
URE range
number setting |
Test voltage
and frequency |
URE measu-
rement range |
URE in
Nominal value |
dication
Permitted deviation |
|
---|---|---|---|---|---|
Signal genera-
tor setting |
Attenua-
tor setting |
||||
08 | 3.162 V 10 kHz | 10 dB | 3 V | 3.162 V | +0.5% |
Adjust URE indica in calibration. | tion to re | ference val | ue obtained | ||
3.162 V 10 MHz |
10 dB
(3 W) |
3 V | 3.162 V | +4% | |
09 | 10 V 10 kHz |
10 dB
(3 W) +10 dB attenua- tor |
10 V | 10.000 V | + 0.5% |
Adjust URE indica in calibration. | tion to re | ference val | ue obtained | ||
10 V 1 MHz |
10 dB
(3 W) +10 dB attenua- |
10 V | 10.000 V | + 0.7% | |
3 MHz
10 MHz |
10.000 V
10.000 V |
+1.5%
+4% |
|||
10 |
10 V 10 kHz
1 MHz 10 MHz |
30 V |
10.00 V
10.00 V 10.00 V |
+0.5%
+0.7% +4% |
URE settings:Operating mode:ACDisplay modes:V and AdBFilters:SLOW (FAST out)Measurement range:Set 100 mV range by use of service function 2<br/>(section 2.3.3.7.2) with entry of range number 05.Test procedure:Test setup as in Fig. 3-1.
URE settings |
Test voltage
and frequency |
URE indi
Nominal value |
cation
Permitted deviation |
Illuminated
display field |
---|---|---|---|---|
LOW PASS out | 100 mV 100 Hz | 100.00 mV | + 0.5% +) | |
LOW PASS in
SELECT 4 kHz |
100 mV 100 Hz
Store indicated v |
100.00 mV
value as re |
+0.5%
+)
ference, with S |
LP/kHz 4
SHIFT, STO. |
Display mode ∆dB |
100 mV 100 Hz
1 kHz 4 kHz 8 kHz |
0.00 dB
0.00 dB -3.00 dB -12.00 dB |
+0.02 dB
+0.04 dB typ. +0.5 dB +1 dB typ. |
LP/kHz 4 |
SELECT 20 kHz,
Display mode V |
100 mV 100 Hz
Store indicated v |
100.00 mV
value as re |
+0.5% +)
ference, with S |
LP/kHz 20
SHIFT, STO. |
Display mode ∆dB |
100 mV 100 Hz
4 kHz 20 kHz 40 kHz |
0.00 dB
0.00 dB -3.00 dB -12.00 dB |
+0.02 dB
+0.04 dB typ. +0.5 dB +1 dB typ. |
|
SELECT 100 kHz
Display mode V |
100 mV 100 Hz
Store indicated v |
100.00 mV
value as re: |
+0.5% +)
ference, with S |
LP/kHz 100
SHIFT, STO. |
Display mode ∆dB |
100 mV 100 Hz
20 kHz 100 kHz 200 kHz |
0.00 dB
0.00 dB -3.00 dB -12.00 dB |
+0.02 dB
+0.04 dB typ. +0.5 dB +1 dB typ. |
LP/kHz 100 |
+) Typical deviation of the four settings from one another < 0.05%.
Check of switching characteristics of the lower cutoff frequencies and associated filtering of the rectified AC voltage.
URE settings:
Operating mode: AC Display mode: v Measurement range: Set 100 mV range by use of service function 2 (section 2.3.3.7.2) with entry of range number 05.
Test Procedure: Test setup of Fig. 3-1:
Table 3-5
URE setting |
Test voltage
and frequency |
7 |
URE ind
Nominal value |
ication
Permitted deviation |
Deviation
range |
---|---|---|---|---|---|
SLOW
(= FAST out) |
100 mV 10 H
100 H 10 k |
łz
iz cHz |
100.00 mV
100.00 mV 100.00 mV |
+2%
+0.5% +0.5% +) |
+2 digits |
FAST |
100 H
50 H 1 k 10 k |
iz
iz cHz cHz |
100.00 mV
100.00 mV 100.00 mV 100.00 mV |
+1%
+0.5% +0.5% +) |
+1 digit
+10 digits typ. |
SUPERFAST
(set manually with use of service |
1 k
500 H |
(Hz
Iz |
100.00 mV
100.00 mV |
+ 1% |
+1 digit
+10 digits typ. |
function 3) | 10 k | Hz | 100.00 mV | ±0.5% +) |
+) Typical deviation of the three settings from one another < 0.05%.
3.2.2.5.1 Linearity of Measured Values
URE settings: | |
---|---|
Operating mode: | AC |
Display mode: | v |
Filters: | LOW PASS out, FAST |
Measurement range: | Set 1 V range by use of service function 2 |
9 | (section 2.3.3.7.2) and entry of range |
number 07. | |
Test procedure: | Test setup of Fig. 3-1 |
- Set the AC calibrator to a frequency | of 10 kHz and the required |
sinusoidal voltage to 1 V and apply the signal to URE input.
Indication on URE: 1.0000 V + 0.5 %
Table 3-6
Test voltage (at 10 kHz) | URE indication | |||||
---|---|---|---|---|---|---|
Nominal value | Permitted deviation | |||||
1.1 V | 1.1000 V | +0.1% | ||||
1.0 V | 1 | 1.0000 V | +0.01% (reference value) | |||
0.9 V | 1 | .9000 V | +0.1% | |||
0.8 V | * (*) | .8000 V | +0.1% | |||
0.7 V | .7000 V | +0.1% | ||||
0.6 V · | .6000 V | +0.1% | ||||
0.5 V | .5000 V | +0.1% | ||||
0.4 V | 1 | .4000 V. | +0.1% | |||
0.3 V | .3000 V+ | +0.1% typ. | ||||
0.2 V | 1 | .2000 V | +0.2% typ. | |||
0.1 V | .1000 V + ) | +0.5% typ. |
+) Blinking of the rightmost digit signifies that the measurement was not made with the optimal measurement range (measured voltage below lower limit of measurement range).
URE settings: As in section 3.2.2.5.1. Test procedure: Test setup Fig. 3-4.
Form of test
signal |
Crest
factor Vp/Vrms |
Test
voltage Vrms |
U
Nominal value |
RE indicat:
Permitted absolute |
ion
deviation relative to sinewave |
---|---|---|---|---|---|
sinewave,
continuous +) Adjust t |
√2
∴o referenc |
1.1 V
e value of |
1.1000 V
AC calibr |
+0.5% +)
ation. |
|
sinewave bursts,
burst duration: 5 ms |
2 | 1.1 V | 1.1000 V | + 0.5% | + 0.1% |
sinewave bursts,
burst duration: 2.2 ms |
3 | 1 . 1 V | 1.1000 V | + 0.5% | + 0•2% |
sinewave bursts,
burst duration: 0.8 ms |
5 | 1.1 V | 1.1000 V | +3.5% | + 3% |
URE settings:
Operating mode: | DC |
---|---|
Display mode: | v |
Filters: | FAST |
Measurement range: automatic (RANGE HOLD out)
Test Procedure:
Test setup Fig. 3-5.
Table 3-8
Output voltage
of DC calibrator |
Attenuator
setting |
DC test
voltage |
URE measure-
ment range |
URE ind
Nominal value |
ication
Permitted deviation |
---|---|---|---|---|---|
- | - |
O V
only 50 Ω termina- tion at UR |
10 mV
E |
.000 mV | +10 digits |
approx. 0.8 V | 40 dB | 8 mV | 10 mV | 8.000 mV |
+(0.1% +
10 digits) |
Set DC calibrator to nominal value of input voltage.
80 mV | - | 80 mV | 100 mV | 80.00 mV |
+(0.1% +
10 digits) |
---|---|---|---|---|---|
0.8 V | - | 0.8 V | 1 V | .8000 V |
+(0.1% +
10 digits) |
8 V | - | 8 V | 10 V | 8.000 V |
+(0.1% +
10 digits) |
80 V | - | 80 V | 100 V | 80.00 V |
+(0.1% +
IO digits) |
300 V | - | 300 V | 300 V | 300.0 V |
+(0.1% +
IO digits) |
URE settings: | |
---|---|
Operating mode: | DC |
Display mode: | V |
Measurement range: | Set 1V range by use of service function 2 |
(section 2.3.3.7.2) with entry of range number 07. | |
Test procedure: | Test setups as in Fig. 3-5 (section 3.2.3.1) and |
Fig. 3-1. |
URE setting | Test signal |
URE
Nominal value |
indication
Permitted deviation |
---|---|---|---|
SLOW |
1 V DC
0.3 V 10 Hz |
1.0000 V
.0000 V |
+(0.1% + 10 digits)
+100 digits +(2 digits typ. as ripple) |
FAST |
1 V DC
0.3 V 100 Hz |
1.0000 V
.0000 V |
+(0.1% +10 digits)
+10 digits +(2 digits typ. as ripple) |
SUPERFAST
(Set with use of service function 3) |
1 V DC
0.3 V 1 kHz |
1.0000 V
.0000 V |
+(0.1% +10 digits)
+10 digits +(2 digits typ. as ripple) |
URE settings: | |
---|---|
Operating mode: | AC+DC |
Display mode: | V |
Filters: | LOW PASS, SELECT 100 kHz, FAST |
Test procedure: | Test setup of Figs. 3-1 and 3-5 (section 3.2.3.1): |
- Apply the signals | from the AC and DC calibrators to URE input. |
- Check the URE indication against the values in Table 3-10.
URE range setting | Input |
URE
Nominal value |
indication
Permitted deviation |
|
---|---|---|---|---|
automatic
(RANGE HOLD out) |
1 V | 10 kHz | 1.0000 V | +(0.5% +10 digits) |
RANGE HOLD |
1 V
1 V |
10 kHz
DC |
1.0000 V | +(0.5% +10 digits) |
The input impedance of the URE is 10 MΩ +2% for DC and low-frequency AC inputs.
The check is unnecessary if the error limits of the AC and DC measurement ranges lie within the permitted deviations.
Only the input capacitance is to be checked.
URE settings:
Operating mode: | AC or AC+DC |
---|---|
Filters: | FAST |
Measurement range: |
Manually set by use of service function 2
with input of range number specified in Table 3-11. |
- Measure the input capacitance.
-----
URE setting | Measurement range | Input ca | pacitance |
---|---|---|---|
Range number | Typical | Permitted | |
05 | 100 mV | 35 pF | < 40 pF |
. 07 | 1 V | 32 pF | < 40 pF |
1 |
3.2.6 Check of Relative Functions
See also sections 2.3.3.2.1, 2.3.3.2.2, 2.3.3.3 and 2.3.3.7.1.
URE settings:
SHIFT key: | not activated |
---|---|
Operating mode: | AC |
Display mode: | v |
Filters: | LOW PASS out, FAST |
Measurement range: | automatic (RANGE HOLD out) |
Test procedure: Test setup of Fig. 3-1:
The indicated value must be retained by operating the SHIFT key. By operating the STO key (second functions level), the retained value is to be stored as reference value for the relative functions \Delta V, \Delta, \Delta B and V/REF.
See also sections 2.3.3.2.1 and 2.3.3.2.2.
URE settings: See section 3.2.6.1. Test procedure: Test setup of Fig. 3-1:
URE setting/entry | Test voltage |
URE ind
Nominal value |
ication
Permitted deviation |
---|---|---|---|
Display mode V |
Set to nominal
URE indication |
223.6 mV | - |
Store 50 Ω as reference
impedance (section 2.3.3.2.1) |
(no change) | 50 . N | |
Display mode dBm | .00 dBm | - | |
Store 500 Ω as
reference impedance |
500. Ω | - | |
Display mode dBm | 20.00 dBm | +0.02 dBm | |
Display mode V |
Set to nominal
URE indication |
1.0000 V | - |
Display mode dBV | (no change) | .00 dBV | +0.02 dBV |
Store measured value
as reference, using SHIFT, STO. |
.00 dBV | +0.02 dB | |
Display mode ∆dB | .00 dBA | +0.02 dB | |
Store 1000 Ω as
reference impedance |
1000.Ω | ||
Display mode dBm | .00 dBm | +0.02 dBm |
3.2.7 Check of IEC-bus Interface
(with built-in IEC-bus option URE-B1)
See also section 2.3.4.
A changed address setting or a switchover from TALK-ONLY to NORMAL is read in either after the URE is switched off and then on again or when service function 1 is called again. The new setting or mode goes into effect only after this has been done.
3.2.8 Check of Analog ( | Output |
---|---|
(with built-in analog output | t option URE-B2) |
URE settings: | |
Operating mode: | DC |
Display mode: | V |
Filters: | FAST |
Voltage measurement range: |
Set 1 V range by means of service function 2
(section 2.3.3.7.2) and entry of range number 07. |
Test procedure:
Displayed value
on URE |
Voltage at
Nominal value |
analog output
Permitted deviation |
---|---|---|
1.0000 V | +1.0000 V | + 2 mV |
-1.0000 V | -1.0000 V | + 2 mV |
.0000 V | 0 V | +2 mV |
No periodic electrical maintenance is required if the instrument is used in normal operating conditions. To insure full functioning, it is recommended that the unit be put through an autocalibration cycle now and then and that the lithium buffer battery and the reference voltages be checked every year or two.
The URE is provided with a microprocessor-controlled self-calibration routine which permits an exact determination of the amplification characteristics, the voltage divider factors, the rectification characteristic of the rmsvalue rectifier and the analog-to-digital conversion factors. These parameter values are determined by comparison with reference DC voltages and from derived AC voltages. The parameters are evaluated by the microprocessor and then stored in a CMOS-RAM. When the URE is switched off, power for the CMOS-RAM is supplied by a buffer battery. Stored autocalibration values can thus be preserved for years.
Autocalibration can be initiated manually by use of service function 4 and via the IEC-bus.
With normal operation of the URE, frequent autocalibrations are not required, since the functional groups of the URE have a high inherent stability.
An autocalibration cycle is required
Preconditions for performing an autocalibration:
- Ambient temperature +20° to +25°C.
- URE fully warmed up to the operating temperature - switched on for at least 30 minutes.
If exceptionally, as in IEC-bus measurement systems, these conditions are deviated from, an increase in error limits is to be expected.
- Call service function 4 (sections 2.3.3.7.2 and 2.3.4.3.5, Table 2-9).
The display CAL appears on the URE.
The autocalibration routine is completed in 20 seconds and the URE returns automatically to the measurement function.
- Replace shorting link BU33.
A CMOS-RAM with buffer battery provides for the preservation of stored reference and calibration values when the URE is shut off.
The lithium battery has a life expectance of typically 10 years. A check of the battery should be made every two years as follows:
To replace the lithium battery,
Since the DC reference voltages used in the autocalibration determine to a large extent the error limits of the URE, they should be checked occasionally. This can conveniently be done when the lithium battery is checked, at intervals of one or two years.
The conditions for checking these voltages and possibly adjusting them are covered in sections 5.2.7.7 and 5.3.1.1.
With normal operating conditions, the URE does not require any mechanical maintenance.
The following recommendations are. however. made:
If the front panel becomes soiled, it can be cleaned with a soft rag moistened with alcohol.
All screws, cables and plug-in units should be firmly seated. The connection of the outer conductor of the ENC socket with the ground of the analog circuit must be sound.
The URE can be stored for longer periods at temperatures between -25°C and +70°C (IEC-359 Application Class 1).
After prolonged storage at high humidities, the instrument should be dried out in the switched-off state at a temperature of about-40°C before being placed in operation.
Fig. 3-1 AC test setup Sinewave Veff: 30 mV to 300 V Frequency: 10 Hz to 100 kHz (1 MHz)
Fig. 3-2 AC test setup Sinewave Veff: 50 µV to 1 V Frequency: 10 kHz to 20 MHz
Fig. 3-3 AC test setup Sinewave Veff: 1 V to 10 V Frequency: 10 kHz to 20 MHz
See Block diagram, Fig. 4-1, and Circuit diagram 342.1214 S.
RMS Voltmeter URE consists of the analog, digital and display/operation functional groups.
In the analog section, the input signal being measured is first processed according to its voltage level in input dividers, wideband amplifiers and range attenuation elements.
The DC and AC components of the input signal are then separately processed in the DC and AC measurement circuits. The AC circuit includes switchable low-pass filters for limiting the measurement bandwidth, switchable highpass filters for eliminating the DC component and adapting the circuit to the measurement speed, a wideband push-pull amplifier, and a square-law measurement rectifier with switchable active filters.
In the DC circuit, the DC component is amplified and the AC component at the same time suppressed with switchable active filter.
The outputs of the two measurement circuits can be alternately switched into a microprocessor controlled A/D converter.
The URE can thus measure the value of the DC component alone, the RMS (or effective) value of the AC component, or the RMS value of the combined AC+DC signal.
The measurement circuits are calibrated automatically under microprocessor control by use of AC and DC reference voltages produced in the analog section.
All analog functions are remotely controllable via analog switches (FET, relays). By the transmission of all control signals over optical couplers and through the use of a separate power supply, the analog section is electrically isolated from the computer section and the instrument chassis.
In the digital section, the microprocessor system consisting of an 8085 microprocessor and peripheral ICs, controls the overall operation of the URE. The functions performed are as follows:
The system program for the microprocessor is stored in four EPROMs of type 2732 with a total capacity of 16 K x 8 bits.
In addition to the microprocessor system, the digital board contains the power supply for the digital, display/operation and analog sections as well as the optocouplers for the voltage-isolated transmission of control and interrogation information to and from the analog part.
The IEC-bus and analog-output options are assigned to the digital section as functional plug-in units.
The display/operation section contains the keyboard and the LED display system with the 4-1/2-place digital display, the circularly arranged quasianalog display, the illuminated displays and key illumination. The inputs to the displays and the interrogation of the keys are time-multiplexed via the computer board by the display-keyboard IC 8279 and microprocessor.
The power supply, consisting of the power switch, combination mains-connector, voltage-selector, fuse holder and power transformer is mounted on the rear panel.
Circuit Diagram 342.2010 S
The microprocessor B1 provides the overall control of RMS Voltmeter URE. To define the start of program execution, about 100 ms after instrument switch-on, the processor receives a signal on its reset terminal from the 5-V voltage monitor T12. B38.
The microprocessor system clock is provided by the squarewave generator with 6-MHz crystal oscillator Ql integrated in the Bl. The derived 3-MHz clock provided on the Bl clock output is used for synchronous control of the peripherals.
Microprocessor 8085 transmits the low-order byte of the address bus and the 8 bits of the data bus in time-multiplexed operation. The low-order addressbyte is selected by the ALE signal of the microprocessor via octal latch B24 as address buffer store. The complete 16-bit address bus is formed from the buffer-stored address byte AØ-A7 and address byte A8-A15 on terminals 21-28 of the 8085.
The assignment of the 16-bit address blocks to the memories and system peripherals is done by decoding address bits A12, A13 and A14 in decoder B21 (Fig. 4-2).
The execution sequence of the microprocessor system is determined by the program stored in the EPROMs B17-B20, which have a total capacity of 16K bytes.
The main memory of the microprocessor consists of the 1K x 4 bit CMOS-RAM B22 and 256 x 8 bit RAM of peripheral IC B2. When the URE is switched off, the lithium buffer battery BA1 supplies the power needed by the CMOS-RAM. The stored reference and calibration values of the URE are thus preserved.
The program and main memory are accessed via the 8-bit data bus of the microprocessor under control of the RD and WR lines. The direction of data transfer is controlled by line RD to data-bus driver B25.
The input and output of control information occurs via the input/output ports of peripheral IC B2. The state of line A15 routed to terminal IO/M determines whether the input/output ports or the RAM area of IC B2 is addressed.
PAØ-PA7 are programmed as output ports and serve for the transmission of all setting data to the analog section via drivers B13 and B14 and optocouplers B4-B12. PBØ-PB6 are also output ports and are used for outputting a voltage value at the analog output (Option URE-B2).
PB7 can be interrogated as an input port. It serves for the recognition of the plug-in status of socket BU33. For measurements, BU33 is plugged to ST33. For service operation the shorting bridge BU33 must be removed. The microprocessor notes the service status via PB7 and enables the call of special service functions.
If the IEC-bus option is present, the microprocessor reads in the IEC-bus address set on the address switch via B2 ports PCØ-PC4 after the instrument is switched on. This also occurs after a call of service function 1 for a display of the IEC-bus address. At the same time, the NORMAL/TALK-ONLY switch setting is detected via port PC5.
For the function setting of the analog section, the processor delivers binary coded data to the 8-bit port A of IC B2. These signals are transmitted to the analog section via the optocoupler interface, decoded after application of an enabling pulse, and transferred to the buffer stores for the function setting. The enabling pulse is provided by the microprocessor to the analog section via the serial output port SOD and optocoupler B4.
During the microprocessor-controlled analog-to-digital conversion, the microprocessor reads in the status of the comparator from the analog section via the serial input port SID and optocoupler B3. Dependent on this information, the position information for the 16-bit D/A converter is output via port A of B2.
Peripheral IC B16 notes by means of its selection logic when a key has been pressed and causes the microprocessor via interrupt line RST5.5 to read in the code of the selected key via the data bus. Unit B16 also provides the complete output control in time-multiplex operation for the LED display elements.
The B16 clock output signal RSØ from pin 32 also controls the TIMER input Ti of IC B2. The TIMER is programmed so that output TO has a frequency 1/7-th that of the Ti signal. The 119.579-Hz pulse signal controls interrupt input RST7.5 of the microprocessor. For the SLOW setting of URE measurement speed, the microprocessor is caused to request measured values from the analog section synchronous with the timing of the control signal at RST7.5. This serves for exact acquisition of measured values for digital filtering.
In addition to the complete microprocessor system, the computer board contains the rectifying circuits and voltage regulator for the supply voltages to the computer, display/operation and analog sections.
The computer requires only the 5-V supply stabilized in B34. When the URE is switched off, the power for the CMOS-RAM B22 is supplied by the lithium battery BA1. In this quiescent condition, the CMOS-RAM draws a minimum current at about 3 V and retains the stored data. When the URE is switched on, the CMOS-RAM is supplied from the 5-V supply via R16, G17 and G11. Switchover from one mode to the other occurs automatically via G12 and G17.
The input voltage of the 5-V regulator B34 is monitored by G114 via R70, G18, R50 and T12.
The monitoring circuit has a response threshold of about 9.5 V at rectifier Gl14. Below this level the 5-V regulator and hence the microprocessor operate satisfactorily. Below this threshold, transistor Tl2 is blocked and prevents, via B38I and B32II, erroneous writing into or erasing of data in the CMOS-RAM while the URE is switched off. When the latter is switched on, the monitoring circuit enables the CMOS-RAM for writing and a reset pulse via R38 initiates the start of the microprocessor. The reset pulse is also sent during service operation at the end of a signature analysis, via B32II, C52 and B38III, IV. These circuit features assure the protection of the reference and calibration data stored in the CMOS-RAM.
The power supplies of the analog section, including rectifier Gl15 and series regulator B35, B36, B37 for stabilizing the 5-V, +15-V and -15-V supplies, are fed from the various windings of the power transformer. The windings are furthermore separated by double screening in the transformer from the mains and the digital section.
IC B1 (8291 A) is connected with the microprocessor data bus and permits data interchange with the peripheral devices via the IEC-625 interface on the rear panel of the instrument.
Data transfer in both directions is provided for, under interrupt control, via the write and read registers of IEC-bus IC Bl. The standard termination of the eight data lines, five control lines and three handshake lines is
provided by the bidirectional drivers B2 - B5, which are connected via BU5/ST5 and flat cable with the IEC-bus board and the 24-contact IEC-bus socket BU7. The IEC-bus address is set in 5-bit code by means of switch S25 on the rear panel of the instrument. The URE can thus be assigned any primary address from decimal 0 to 30. An additional setting of switch S25 permits the choice between addressed IEC-bus transfer (NORMAL function) and the TALK-ONLY function. In the latter case, a value displayed on the URE can be output to a LISTEN-ONLY device of the bus system without addressing by pressing a key on the URE.
A signature analysis is provided in the URE for checking the microprocessor system.
The signature analysis is activated by repositioning the shorting bridge BU19 on ST19.2/3. This causes the processor to cyclically run through its entire address space.
The data transfer from processor to program memory is in this case interrupted by bus driver B25, and driver B26 is activated and generates a NOP instruction with every read cycle of the processor. The start-stop signals for the signature analyzer are derived directly from the address bus via B27 IV.
For the signature analysis of the data bus only stationary memory data may be used, in order to obtain unequivocal indications as to the functioning of the circuit.
During the signature analysis, readout of data from peripherals 8155, 8279 and 8291A is therefore prevented via gate units B32 III, B31 II, RDconnection and from the CMOS-RAM via B32 III, B32 I, B32 II, CE-connection. After completion of the signature analysis, repositioning of shorting bridge BU19 results in a reset pulse to the microprocessor via B32 III, C52, B38 III and B38 IV.
4.2.4 Analog Output (Option URE-B2) Circuit Diagram 342.2810 S
In every display cycle a corresponding DC voltage is applied to the analog output.
A display value computed by the processor in binary form is divided by 10 and transmitted in two steps of 6 bits each via output port PBØ-PB6 of IC 8155. The intermediate storage in unit B14 provides the 12-bit input for D/A converter B15, which thus provides an analog output of 1 mV/least significant bit at analog output BU1/BU2. The voltage output range lies between -2.048 V and +2.047 V. Potentiometers R43 and R45 are used for the exact adjustment of the D/A converter.
The +15-V inputs to the D/A converter are derived from the 5-V regulated supply of the computer section via converter circuit B33, T13, T15, TR1 with 18-kHz frequency, appropriate transformation, rectification and stabilization with B31 and B32.
4.3 Display Board
Circuit Diagram 342.2410 S
The display board contains
The reading of the keyboard and outputting of the display information is done in time-multiplex operation via the display-keyboard IC 8279 and the microprocessor.
For key recognition, IC 8279 generates clock signals on RSØ-RS2 derived from the 3-MHz microprocessor clock. After decoding in Bl1, the signals are applied to key matrix S1-S18 which is sampled every 4.8 msec with a pulse width of 0.6 msec for each selection line. If a key is pressed, the clock signals go onto one of the return leads R10, R11, R12 which are in turn interrogated by the 8279. After recognition of a pressed key, the 8279 reports the event via the interrupt line to the processor, which can read in the key code as determined by a matrix via the data bus. The 8279
provides for an electronic debounce of the key contacts and so assures an error-free input.
The signals on RSØ-RS3 are decoded in the 4-in-16-line decoder B10 for output to the front-panel display elements.
The drive signals for the LED groups such as the 7-segment digital display B1-B5 and illumination fields B6, B7 are supplied via 15 output lines. The key illumination G115 - G122 and G1 25 is fed in each case via two selectable lines, one of which yields an enhanced illumination.
For the activation of a single segment of an LED group, an 8-bit signal is sent from the 8279 to the display board via lines AØ-A3 and BØ-B3.
To every line is assigned a specific segment of the group. The segment is activated via driver transistors T10 to T17.
By synchronous control of the group- and segment-selection signals, each individual segment of the LED display can be activated.
By periodic activation every 9.6 msec, it is assured that the display elements do not flicker.
4.4 Analog Board Circuit Diagram 342.2210 S
The analog board has the function of processing the voltage being measured. It comprises the following circuit functions:
For AC voltage measurements, capacitor C6 in the input circuit separates the DC component of the incoming signal. In the DC and AC+DC operating modes, this capacitor is shorted out by relay RS1. Depending on its size, the input signal is passed via relay RS2 to the high-resistance 10-M input-voltage divider with the 1-dB step or the divider with the 41-dB/61-dB step.
Trimmers C8, C13 and C15 serve for frequency-characteristic compensation in the low-frequency range and potentiometer R4 for correction in the higher frequency range of the URE.
MOSFETs T31 - T33 switch the three divider outputs to the wideband input amplifier (Table 4-2).
In DC and AC+DC measurements, an offset comparison of the amplifier branch is made periodically. Depending on the measurement range, resistor R118 may thus be switched to the amplifier input through relay RS3 (see section 4.4.2.3). In the 1-dB divider stage, FET diodes in the input network together with R14, C16 and C18 limit the input voltage range to protect the analog switch and input amplifier.
This amplifier, with high-impedance FET input stage T6, is designed as an operational amplifier with differential stages. Dual-transistor T5 serves as active load for the FET input stage.
To match the measurement sensitivity of the URE, the input amplifier is switchable to 6-dB and 26-dB gain via analog switch B40 (Table 4-2).
The gain values are determined by feedback resistors R80 - R82 and are adjusted at the upper band limit with trimmers C21, C24.
With use of the 8-bit D/A converter B2 II, B3 and R45 - R58, the offset voltage can be automatically adjusted under microprocessor control. The microprocessor thus changes the input data to the D/A converter in binary steps until the offset voltage of the entire DC measurement section does not exceed the limit set by the 8-bit resolution.
The low-resistance range divider with attenuation levels 0/10/20/30 dB provides additional matching to the large dynamic range of the input voltage. From the various combinations of the input divider and input amplifier, a division of the URE input voltage range into twelve 10-dB subranges is brought about (Fig. 4-4, Table 4-2).
The buffer amplifier, consisting of IC B9 and transistors T18, T19, T21, T22 and T30 amplifies the divider output signal by 4.5 dB. The amplifier gain is determined by feedback resistors R136 and R135. Elements C88, C125 and R87 correct the frequency characteristic at the upper band limit.
The buffer amplifier provides decoupling of the following low- and high-pass filters of the attenuators of the range dividers. Following this stage, the signal is separately processed in the AC and DC branches.
In the AC measurement circuit a low-pass filter may be switched in by means of FET switches T49 and T55 to limit the bandwidth of measurement. For full bandwidth, the direct signal path via FET switch T50 is cut in.
The low-pass filter with opamp B6 is an active 2nd-order Butterworth filter. A cutoff frequency of 4, 20 or 100 kHz is selected by activation of FET switches T46, T54, T58 and T57 (Table 4-2).
Three high-pass filters may be switched into the signal path to adapt the AC circuit to the measurement speed. These consist of the capacitors C44 (for f > 1000 Hz, SUPERFAST speed), C46 (for f > 100 Hz, FAST speed) and C45 (for f > 10 Hz, SLOW speed) in conjunction with resistors R280 and R281. The filter selection is made with B36 I, III, IV (Table 4-2).
After frequency-band limiting by the low- and high-pass filters, it is necessary to amplify and balance the signal before it goes to the measurement rectifier. This is done in the push-pull amplifier, which has a gain of 20 dB. To shorten the transient period in the rectifier, the amplifier
is DC coupled to the rectifier. This in turn requires small offset and drift values of the amplifier for satisfactory transmission of the signal to the rectifier.
The push-pull amplifier comprising ICs B17 and B18 and transistors T23 - T26 delivers amplified signals of opposed phase at the output stages. The inphase signal, amplifier 14 dB, lies at the output B18II, T25, stabilized by direct negative feedback coupling via R164 and R183 to the B17 input stage. A sum signal derived from both outputs is produced by means of R184, R190, R191 and represents a measure of the output asymmetry. It acts on the collector circuit of the input stage by means of a correction current fed in through stage B17I and determines the symmetry of the output (Fig. 4-3). Pot R174 serves for the zero adjustment of the offset voltage.
Input stage, symmetry stage, amplifier and output stages
Fig. 4-3 Functional diagram of push-pull amplifier
The passive bridge circuit made up of dual FET T27 I, II has the function of forming the RMS value of the AC component of the voltage being measured. The input to the bridge consists of the two phase-opposed outputs of the push-pull amplifier. The bridge circuit performs the squaring of the input signal, the rectified voltage output being given by the simplified formula
where
Pot R195 is used for compensating small symmetry errors of the two phaseopposed inputs and the rectifier bridge. The symmetrically connected lowpass filter R199, R200, C65 - C67 suppresses the higher frequency components of the rectified signal.
The circuit consisting of the differential amplifier B20 - B22 and the operational amplifiers B23 I, II provides amplification and the filtering low frequency components of the rectified signal. The amplification of the differential amplifier can be adjusted with R201 and R202 in four coarse steps. The large spread in the rectification factor of the FET rectifier is thus taken into account in the adjustment of URE.
The amplifier circuit functions as an active, switchable, low-pass filter. In FAST and SUPERFAST measurements it forms a 3rd-order filter with a pole in amplifier B20, B21 and two poles in the active low-pass filter formed with B23I.
In SLOW measurements, the circuit with switch-in of capacitor C76 forms essentially a 1st-order filter. Together with a software based recursivedigital filter of 3rd order, a 4th-order filter results with particularly good transfer characteristics.
The advantages are the optimal setting behaviour and the suppression of the low-frequency components down to the measurement frequency of 10 Hz (dielectric error effects of large filter capacitors are avoided).
Through the input of the 10-V DC voltage via amplifier B22 a level shift of -8.4 V results at rectifier output ST2.2. This provides for optimal utilization of the bipolar voltage range of the 16-bit D/A converter B25 (see 4.4.1.10).
The rectifier DC output voltage goes via FET switch T51 to comparator B24 and after microprocessor-controlled A/D conversion (successive approximation) is further processed in the computer section of the URE (see section 4.4.2).
After passing through the buffer amplifier, the DC component of the measured signal is further processed in the DC measurement circuit, consisting of amplifier B10 in conjunction with active low-pass filter stages. The amplification factor of 76 is determined by the feedback coupling R125, R133.
The active filters serve for the suppression of the AC components of the measured signal. The cutoff frequencies are set by MOSFETs T41 - T44 in accordance with the selected measurement speed (Table 4-2). Filters of different orders result as follows:
The output voltage of the DC measurement circuit passes through FET switch T52 to comparator B24 for microprocessor-controlled A/D conversion.
The circuit formed by Gl25 and Gl134 functions when FET T53 is switched in, as limiter of negative output voltages falling below -8 V. This prevents possible overdriving of the DC amplifier influencing the evaluation of the AC channel.
After preprocessing, the voltage being measured is converted to digital form by means of successive approximation carried out in the analog section by comparator B24 and 16-bit D/A converter B25 with input circuits B26, B27, B28, B30 and B31.
The microprocessor is connected via the optocoupler interface. The processor applies data stepwise to the D/A converter, beginning with the most significant bit. The comparator compares the resultant output of the converter with
the output voltage of the AC or DC measurement circuit. After every such step, the processor reads the logical state of the comparator output via an optocoupler into the serial input port SID. It is then tested whether the set input bit of the D/A converter is correct or not. This process is continued to the least significant bit (16th bit). Every correctly set bit is summed by the processor corresponding to the binary value.
After completion of the conversion, the measured voltage in digital form with value 0 to 65535 is stored for further use by the microprocessor.
Before each conversion, the microprocessor sends a pulse, via reset line BU3.15, latch units B30 and 31 and inverting drivers B26 - B28 to reset the D/A converter to the start state, i.e. with all bits set to logic 1. This setting corresponds to a D/A converter output of -10 V. The measurement range extends from -10 V to +9.99969 V.
D/A converter B25 also provides the stabilized 6.3-V DC reference voltage for use in deriving further DC and AC reference voltages for the analog section.
Highly stable DC and AC voltage generators are required for the microprocessorcontrolled autocalibration of the analog section.
The DC reference generator processes the 6.3-V reference from the D/A converter to provide, via circuit B2I, T3, a 10-V DC reference, from which resistor network R23 derives the 1-V and 0.1-V DC reference voltages.
The DC reference voltages are adjusted to their rated values with R33, R36 and R39.
With the 4-part analog switch B1, the three DC reference values and zerovoltage reference are applied to the input circuit of the URE. An additional reference voltage of 0.71 V is derived over the resistive voltage divider R17, R27 which can be cut in with T34.
The 0.71-V and 1-V DC references are chopped to produce, via analog switch B14 and timing generator B13, two highly stable AC reference voltages for calibration of the AC measurement circuit. The timing frequency is 5 kHz.
Voltage follower B16 serves to provide a low-impedance input to voltage divider R169, R168, R166, R171. The AC references can be switched with FET switch T56 to the input of the push-pull amplifier. After removal of the DC
component by C49, the effective (rms) value of the generated AC references are 21 mV and 30 mV respectively.
The output voltage of the AC reference branch may be set by R171 for ratedvalue adjustment of the AC indication. By switching off timing generator B13, a zero-voltage reference may be generated via the AC reference branch at the input of the push-pull amplifier for use in calibrating the measurement rectifier.
The microprocessor sends coded control signals to the analog board via the output ports and optocoupler. For assigning place values, the appropriate coded information is transmitted via interface BU3.
The signal bits are applied in parallel to lines BU3.1, 2, 3, 4, 5, 12, 16. The three bits on lines BU3.4/.5/.12 are decoded to select one of the buffers B3, B4, B5, B12, B15, B30 or B31. The three bits of lines BU3.1, 2, 3 serve for addressing the outputs of the 8 buffers. Line Bu3.16 carries the bit identifying the logical state of an addressed analog function.
For the acceptance of the applied coded data by the buffers, the microprocessor outputs a short pulse via serial output port SOD onto line BU3.14. After inversion in unit B62VI, the pulse is applied to decoder B29 to enable decoding of the applied input data. For the duration of the acceptance pulse, decoder B29 outputs on terminals Q0-06 the signal for selecting one of the addressable buffers. The latter decodes the address information on inputs A0-A2 when input line WD goes to 0.
The addressed unit then delivers at the output specified by AØ-A2 the logical state (O V or 5 V) determined by the data bit on the D input.
The transmitted and decoded information remains stored until a new state is selected or the instrument is switched off. 55 individually programmable outputs for controlling the analog functions are thus obtained.
At program start a reset pulse is sent via output Q7 of decoder B29 to reset addressable stores B3, B4, B5, B12 and B15.
The activation of all analog functions proceeds from the stored output states i.e. 0 V or 5 V of the addressable 8-bit latch. The analog switch requires special control levels which are generated with comparators B51, B52, B53, B54, B56, B57, B59 and B60 (Table 4-1). The comparators are driven by the 0 V or 5 V logic signals of the 8-bit latch.
One of the two inputs of each comparator is for this purpose connected with a common line at +2.5 V being derived via R5 and R6 from the 5-V supply.
Table 4-1
Control level for the analog switch
Level | Analog switch |
---|---|
0 V/+15 V | B1, B13, B14 |
±15 V | B40, T31 - T58 |
-7.5 V/+15 V | B36I, III, IV |
In both manual and IEC-bus-controlled operation, the URE performs measurements under microprocessor control. The program includes the following routines:
See also sections 3.3.1 and 5.2.1.2
The URE has a callable routine for calibrating the analog section.
The autocalibration routine selects certain measurement ranges for calibration and provides the zero-reference and DC-reference voltages, which are switched into the input circuit via RS2.
The A/D-converter routine measures the zero and reference output voltages several times in each measurement range. After averaging and forming the difference between reference and zero measurements, the calibration values for ranges 4, 5, 6, 7, 8, 9 and the two auxiliary ranges 13 and 14 are obtained (see sections 5.2.1.2 and Table 4-2). All other measurement-range factors are converted from these values.
This procedure allows calibration of the measurement ranges and the A/D conversion with the accuracy and stability of the three DC reference voltages.
The results of the measurement-range calibration are stored in the CMOS-RAM in the form of A/D-converter step numbers which are then taken into account in the computations associated with a voltage measurement.
The routine also performs a calibration of the RMS rectifier with use of two AC reference voltages and zero reference. For this the voltages are switched in turn to the input of the push-pull amplifier and the output of the square-law rectifier measured by way of the A/D conversion.
The AC reference voltages are derived from the 0.71-V and 1-V DC references (see section 4.4.1.11).
For the autocalibration of the rectifier characteristic, the ratio of the AC voltages must first be exactly determined. Since the amplitudes of the AC voltages are proportional to the DC reference voltages, it is sufficient to determine the ratio of the latter.
For this, as in the range calibration, the 0.71-V DC, 1-V DC and zero references are switched to the URE input circuit and the output voltages of the DC measurement circuit measured using measurement range 6. The ratio is computed by the microprocessor.
The results of the three rectifier calibrations permit the computation of the three characteristic coefficients of the square-law measurement rectifier. The coefficient values are stored in the CMOS-RAM. They are used in a voltage measurement to compute the RMS value of the AC voltage from the output of the square-law rectifier (section 4.4.2.2).
During the calibration, the nominal/actual values are compared with rated values and tolerances provided in the program. If a calibration value exceeds the tolerances, an error message Err 1...15 is displayed on the URE or in remote operation a status byte is sent to the IEC-bus controller (section 5).
A complete autocalibration cycle requires about 20 seconds. The URE then reverts automatically to the measurement mode.
In response to an input of a pair of phase-opposed sinusoid signals within certain tolerances, the FET rectifier bridge T27 I, II produces an output whose mean value is given by the formula
where V is the RMS value of the input voltage.
For the computation of the RMS value, the three parameters V00, b and c of the characteristic must be known. The values of these parameters are determined in the autocalibration by appropriate reference measurements and conversions (section 4.4.2.1).
The coefficient c represents a deviation from a pure square-law characteristic and has a relatively low value. For any particular FET this coefficient is constant and will therefore be only determined once - during the autocalibration.
The coefficients V and b on the other hand are time and temperature dependent to some degree and are therefore periodically determined with appropriate reference measurements.
The periodic calibration of the rectifier is made at regular intervals, the length of the interval depending on the measurement speed to which the URE is set:
For measurement speed SUPERFAST, every 9 sec (approx.) FAST, every 11.5 sec (approx.) SLOW, every 16.5 sec (approx.)
The voltage measurements are interrupted about 170 ms for each calibration.
For the periodic determination of coefficients V00 and b, the AC reference branch is switched to the input of the push-pull amplifier. The voltage under test is thereby disconnected. To prevent cross-talk of higher-frequency components into the reference branch, the inputs to the buffer amplifier and coupling capacitors C44-C46 are also disconnected.
After the zero reference has been produced in the AC reference branch, the first comparison measurement yields the offset voltage for the output of the AC measurement circuit and thus the value of the coefficient V
The second measurement is made with the larger of the two AC reference voltages derived from the 1-V DC reference by chopping. The squarewave voltage, after voltage division and elimination of the DC voltage, is applied to the push-pull amplifier. The size of the AC reference corresponds to the upper limit value of the measurement range involved. The rectified signal provides the value for determining the value of coefficient b.
During the rectifier calibration, the active filters are switched to SUPER-FAST operation in order to perform the calibration as speedily as possible.
The coefficient values are stored and used in subsequent measurements of RMS values.
Pot R171 provides for the setting of a correction factor to adjust to the rated value of the display for a specified AC input voltage.
In DC and AC+DC operation, after every change of the measurement range as well as periodically, the DC measurement circuit is tested and an offset correction made of the entire amplifier branch including the A/D converter. For this purpose, the test voltage input is disconnected from the input amplifier and a zero voltage produced. Incorrect voltage at the output of the DC measurement circuit is detected at the A/D converter output. The value is stored and used to correct all measured DC values.
Additionally, in DC voltage measurements the URE switches momentarily during
every measurement cycle to the AC measurement circuit and monitors the input. When maximum input voltage is exceeded a less sensitive DC range is selected until maximum input is again observed in the AC measurement circuit. Settings of the analog section for offset measurements:
Analog switch
In ranges with 1-dB input dividers: | Relay RS2 switched off; zero-voltage reference provided via analog switch B1 III. |
---|---|
In ranges with 41-dB
or 61-dB input dividers: |
Resistor R118 switched to amplifier input with RS3; FET switches T31 and T32 switched off. |
General: |
Filter in DC measurement circuit set to SUPERFAST
by switching off FET switches T41 - T44. |
The offset correction is made periodically at the same time intervals as the rectifier calibration (section 4.4.2.2). The DC voltage measurement is interrupted for about 100 ms for this procedure.
During every offset measurement, it is checked whether the offset voltage lies within the permitted range of ±1.3 V at the output. If it lies outside this range, offset adjustment of the input amplifier is performed automatically. With the URE set to the 1-mV range, a correction voltage is applied to the input amplifier with the use of the 8-bit D/A converter until the offset voltage at the output of the DC measurement circuit falls within the range corresponding to the 8-bit resolution. This offset adjustment requiring about 340 ms prevents run-away of the offset voltage by, for example, large temperature changes. The adjustment setting of the D/A converter remains stored.
If for any reason the offset voltage cannot be reduced to a permitted value, a functional fault is present. The URE then displays the error message Err 1 (section 5).
The value of the DC voltage being measured is made up of the value measured by the DC measurement circuit, the offset voltage and the calibration values for the measurement range involved.
In the AC+DC measurement mode, the AC and DC measurement circuits are alternately switched to the comparator for A/D conversion.
The AC and DC components of a mixed signal are determined in the AC and DC measurement circuits respectively in the same way as for a pure AC or DC signal.
With correct choice of the measurement range (section 4.4.2.5), the RMS value of the mixed voltage is computed by the microprocessor routine with the equation
In the case of AC+DC measurements, the periodic calibration includes the DC offset correction and rectifier calibration in a single program routine. The combined calibration requires about 240 ms.
Automatic range selection or autoranging is microprocessor-controlled according to the rules given below. It makes possible a rapid, optimal selection of the measurement range.