TTI 1604 schematic

INSTRUCTION MANUAL

1604

40,000 Count Digital Multimeter

Table of Contents

Introduction 2

Specifications 3

Safety 7

EMC 8

Installation 9

General Operation 10

Making Measurements 12

Further Functions 14

Maintenance & Calibration 15

Remote Operation 15

Instructions en Francais 16

Bedienungsanleitung auf Deutsch 25

Istruzioni in Italiano 34

Instrucciones en Español 43

1

Introduction

This true RMS multimeter is a low-cost manual/autoranging bench-top instrument with a large,
bright LED display. It offers 4¾ digit (40,000 count) scale length and a resolution of 10µV and
10mΩ.

The key features are:

• 0.56” (14mm) high brightness LED display.

• 0.08% basic accuracy, 40,000 counts.

• Manual or autoranging.

• DC and AC Volts, DC and AC current, Resistance and Frequency measurement; Continuity

and Diode checks.

• True RMS AC measurement, 4,000 counts.

• Display nulling.

• Touch hold mode - holds onto a stable reading until updated.

• Remote control and data-logging to disk using optional Windows software.

• Fully compliant with EN61010-1 Safety and EN61326 EMC standards.

TEST EQUIPMENT RISK ASSESSMENT

Recommendation from the U.K. Health and Safety Executive

Users of this equipment and or their employers are reminded that Health and
Safety Legislation require them to carry out valid risk assessments of all electrical
work so as to identify potential sources of electrical danger and risk of electrical
injury such as from inadvertent short circuits. Where the assessments show that
the risk is significant then the use of fused test leads constructed in accordance
with the HSE guidance note GS38 ‘Electrical Test Equipment’ for use by
electricians’ should be used.

2

p

ACCURACY

Accuracies apply for 1 year 19°C to 25°C. Temperature coefficient outside these limits is
<0.1 x quoted range accuracy per °C.

DC Volts

Range Accuracy Resolution Notes

Specifications

400mV 0.08% ± 4 dig. 10µV

4V 0.08% ± 4 dig. 100µV

40V 0.08% ± 4 dig. 1mV DC/AC pk.

400V 0.08% ± 4 dig. 10mV

1000V 0.09% ± 4 dig. 100mV

AC Volts (True RMS)

Range Accuracy Resolution

45Hz - 400Hz 400Hz - 4kHz 4kHz - 20kHz

400mV 1% ± 4 dig. 2% ± 4 dig. 100µV

4V 1mV

40V 0.5% ± 4 dig 2% ± 4 dig 5% ± 4 dig. 10mV
400V - - 100mV
750V 1% ± 4 dig. - - 1V

Accuracies apply for readings between 400 and 4,000 counts. Additional error at crest
factor = 3 is typically 1%. Input impedance = 10MΩ nominal.
1kΩ unbalanced CMR = >60dB at DC/50Hz/60Hz

265V DC/AC rms max

Max in

ut 1000V

†

.

Input impedance 10MΩ nominal

NMR:>60dB @ 50/60Hz

CMR:>90dB @ DC/50Hz/60Hz†

†

Max. input = 750V rms, 1kV pk. (265Vrms on 400mV range).

Resistance

Range Accuracy Resolution Notes

400Ω 0.15% ± 6 dig.∗ 10mΩ

4kΩ

40kΩ

400kΩ

4MΩ
40MΩ (up to 20MΩ)
40MΩ (up to 40MΩ)

0.1% ± 4 dig.

0.1% ± 4 dig.

0.15% ± 4 dig.

0.3% ± 6 dig.

1.0% ± 10 dig.

2.0% ± 10 dig

∗ after Null

100mΩ

1Ω

10Ω

100Ω

1kΩ
1kΩ

3

Max. input 265V DC or ACrms any range.

Max. open circuit voltage 4V.

†

60Hz rejection is a factory option.

DC Current

Range Accuracy Resolution Notes

400mA 0.1% ± 4 dig. 10µA Voltage burden <500mV
10A (up to 1A) 0.3% ± 4 dig. 1mA
10A (up to 5A) 1.0% ± 4 dig. 1mA Max. input 10A, 250V, fuse protected

4mA 0.1% ± 4 dig. 0.1µA Max. input 1A, 250V, fuse protected

10A (up to 10A) 3% ± 10 dig 1mA

AC Current (True RMS)

Range Accuracy (45Hz - 10kHz) Resolution Notes

4mA 0.5% ± 4 dig. 1µA Max. input 1A, 250V, fuse protected

400mA 0.5% ± 4 dig. 100µA Voltage burden <500mV
10A (up to 1A) 0.8% ± 4 dig. 10mA
10A (up to 5A) 1.5% ± 4 dig 10mA Max. input 10A, 250V, fuse protected

10A (up to 10A) 3% ± 4 dig. 10mA Voltage burden <500mV

Accuracies apply for readings between 400 and 4,000 counts. Additional error at crest factor = 3
is typically 1%.

Frequency

Range Accuracy Resolution Gate Notes

4kHz 0.01% ± 1 dig. 0.01Hz 1s Sensitivity set by
40kHz 0.01% ± 1 dig. 0.1Hz 10s AC range setting

Voltage burden <500mV

Continuity and Diode Test

Continuity:
Diode Test: Test current approximately 1mA at 1V; displays voltages up to 3V.
Maximum Open Circuit

Voltage:
Maximum Input: 265V DC or AC rms.

FURTHER FUNCTIONS

Hold: Reading is frozen
T-Hold (Touch & Hold): Reading is frozen when stable.
Min/Max: Minimum and maximum readings stored.
Null (Relative): Stores current reading and subtracts it from future readings. Up to

4kΩ range selected; audible tone sounds for impedance <10Ω.

4V

±1,000 counts can be nulled without restricting the measurement
range. Counts greater than ±1,000 can be nulled to give a Relative
reading but the measurement range is correspondingly reduced; OFL
shows in the display when the measurement range is exceeded.

4

DISPLAY

Display Type: High brightness LED. Height 0.56” (14mm).
Scale Length: 4¾ digits (40,000 counts); AC ranges 4,000 counts.
Annunciators: For all ranges, functions and program modes.
Reading Rate: 2.5 readings/sec.
Overrange: Display shows OFL if input too great for range.

GENERAL

Power: 110V-120V or 220V-240V AC ±10%, 50/60Hz, adjustable internally;

3VA max. Installation Category II. 60Hz operation is a factory option.

RS232 Interface: Baud Rate 9600. Permits remote control and data-logging to disk using

optional Windows software.
Operating Range: +5°C to + 40°C, 20% to 80% RH.
Storage Range:
Environmental: Indoor use at altitudes up to 2000m, Pollution Degree 1.
Safety: Complies with EN61010-1.
EMC: Complies with EN61326.
Size: 260(W) x 88(H) x 235(D)mm, excluding handle and feet.
Weight: 2.0kg.

−40°C to + 70°C.

5

EC Declaration of Conformity

We Thurlby Thandar Instruments Ltd
Glebe Road
Huntingdon
Cambridgeshire PE29 7DR
England

declare that the

Model 1604 Digital Multimeter

meets the intent of the EMC Directive 2004/108/EC and the Low Voltage Directive 2006/95/EC.
Compliance was demonstrated by conformance to the following specifications which have been
listed in the Official Journal of the European Communities.

EMC

Emissions: a) EN61326-1 (2006) Radiated, Class B

b) EN61326-1 (2006) Conducted, Class B
c) EN61326-1 (2006) Harmonics, referring to EN61000-3-2 (2006)

Immunity: EN61326-1 (2006) Immunity Table 1, referring to:

a) EN61000-4-2 (1995) Electrostatic Discharge
b) EN61000-4-3 (2006) Electromagnetic Field
c) EN61000-4-11 (2004) Voltage Interrupt
d) EN61000-4-4 (2004) Fast Transient
e) EN61000-4-5 (2006) Surge
f) EN61000-4-6 (2007) Conducted RF

6

Performance levels achieved are detailed in the user manual.

Safety
Multimeter: EN61010-1
Installation Category I measurements to 1000V,

Installation Category II measurements to 600V,
Pollution Degree 1.

Probes: IEC1010-2-031
Rated to 1000V, Installation Category III.

CHRIS WILDING
TECHNICAL DIRECTOR

2 May 2009

Safety

This multimeter is a Safety Class I instrument according to IEC classification and has been
designed to meet the requirements of EN61010-1 (Safety Requirements for Electrical Equipment for
Measurement, Control and Laboratory Use). It is an Installation Category II instrument intended for
operation from a normal single phase supply.

WARNING! THIS INSTRUMENT MUST BE EARTHED

Any interruption of the mains earth conductor inside or outside the instrument will make the
instrument dangerous. Intentional interruption is prohibited. The protective action must not be
negated by the use of an extension cord without a protective conductor.

The test leads supplied with this instrument meet the requirements of IEC1010-2-031 and are rated
to 1000V Category III; use only these test leads with the meter or a set of equivalent performance.

This instrument has been tested in accordance with EN61010-1 and has been supplied in a safe
condition. This instruction manual contains some information and warnings which have to be
followed by the user to ensure safe operation and to retain the instrument in a safe condition.

This instrument has been designed for indoor use in a Pollution Degree 1 environment (no pollution,
or only dry non-conductive pollution) in the temperature range 5°C to 40°C, 20% - 80% RH (non­condensing). It may occasionally be subjected to temperatures between +5° and −10°C without
degradation of its safety. It has been designed for Installation Category II measurement use to
600VDC/ACrms and Installation Category I measurement use to 1000VDC/750VACrms. The full
definitions of Categories I and II can be found in IEC664, but the following can be taken as a guide:

Installation Category I is signal level e.g. telecommunication, electronic equipment, with smaller
transient overvoltages than Installation Category II.

Installation Category II is local domestic supply level, e.g. portable equipment and appliances. In
particular, Category II does not include distribution level supplies, e.g. three phase installations
which are classified as Installation Category III.

For this equipment 2500V is the maximum peak transient overvoltage that can be tolerated by any
terminal with respect to earth ground without impairing safety.

Use of this instrument in a manner not specified by these instructions may impair the safety
protection provided. Do not operate the instrument outside its rated supply voltages or
environmental range. In particular excessive moisture may impair safety.

When the instrument is connected to its supply or its inputs are connected to live voltages, terminals
may be live and opening the covers or removal of parts (except those to which access can be
gained by hand) is likely to expose live parts. The apparatus shall be disconnected from all voltage
sources before it is opened for any adjustment, replacement, maintenance or repair.

Any adjustment, maintenance and repair of the opened instrument under voltage shall be avoided
as far as possible and, if inevitable, shall be carried out only by a skilled person who is aware of the
hazard involved.

If the instrument is clearly defective, has been subject to mechanical damage, excessive moisture
or chemical corrosion the safety protection may be impaired and the apparatus should be withdrawn
from use and returned for checking and repair.

Make sure that only fuses with the required rated current and of the specified type are used for
replacement. The use of makeshift fuses and the short-circuiting of fuse holders is prohibited.

Do not wet the instrument when cleaning it and in particular use only a soft dry cloth to clean the
display window. The following symbols are used on the instrument and in this manual:

WARNING - risk of electric shock.

CAUTION - refer to accompanying documentation;
incorrect operation may damage the meter.

7

mains earth (ground)

direct current

alternating current

This instrument has been designed to meet the requirements of the EMC Directive 2004/108/EC.
Compliance was demonstrated by meeting the test limits of the following standards:

Emissions

EN61326-1 (2006) EMC product standard for Electrical Equipment for Measurement, Control and
Laboratory Use. Test limits used were:

a) Radiated: Class B
b) Conducted: Class B
c) Harmonics: EN61000-3-2 (2000) Class A; the instrument is Class A by product category.

Immunity

EN61326-1 (2006) EMC product standard for Electrical Equipment for Measurement, Control and
Laboratory Use.

Test methods, limits and performance achieved are shown below (requirement shown in
brackets):

a) EN61000-4-2 (1995) Electrostatic Discharge : 4kV air, 4kV contact, Performance B (B).

EMC

b) EN61000-4-3 (2006) Electromagnetic Field:

c) EN61000-4-11 (2004) Voltage Interrupt: ½ cycle and 1 cycle, 0% : Performance A (B);

d) EN61000-4-4 (2004) Fast Transient, 1kV peak (AC line), 0·5kV peak (signal connections),
Performance B (B).

e) EN61000-4-5 (2006) Surge, 0·5kV (line to line), 1kV (line to ground), Performance A (B).
f) EN61000-4-6 (2007) Conducted RF, 3V, 80% AM at 1kHz (AC line only; signal

connections <3m, therefore not tested), Performance A (A).
According to EN61326-1 the definitions of performance criteria are:

Performance criterion A: ‘During test normal performance within the specification limits.’
Performance criterion B: ‘During test, temporary degradation, or loss of function or

performance which is self-recovering’.
Performance criterion C: ‘During test, temporary degradation, or loss of function or

performance which requires operator intervention or system reset occurs.’

†

Note: The 1604 is a sensitive measuring instrument and, if subjected to a sufficiently large

radiated RF field, measurements may deviate beyond the accuracy specification at certain
frequencies up to 1GHz. However, possible deviations will be small and infrequent and are not
deemed to be a problem in practice. In all other respects the instrument will operate normally
(Performance A) in fields up to 3V/m.

Cautions

To ensure continued compliance with the EMC directive the following precautions should be
observed:

a) Only use screened cables and connectors to connect between the multimeter’s RS232

interface and other equipment.

b) After opening the case for any reason ensure that all signal and ground connections are

remade correctly before replacing the cover. Always ensure all case screws are correctly
refitted and tightened.

c) In the event of part replacement becoming necessary, only use components of an

identical type, see the Service manual.

†

3V/m, 80% AM at 1kHz, 80MHz – 1GHz: Performance B
Performance A (A); 1V/m, 2.0GHz to 2.7GHz: Performance A (A).

25 cycles, 70% : Performance B (C); 250 cycles, 0% : Performance C(C).

(A) and 1.4GHz to 2GHz:

8

Mains Operating Voltage

Check that the instrument operating voltage marked on the rear panel is suitable for the local
supply. Should it be necessary to change the operating voltage, proceed as follows:

1) Disconnect the instrument from all voltage sources.

2) Unclip the front bezel by gently pulling the centre of each long edge up and forward.
The case halves are held together by 4 plastic push-rivets. Use the blade of a small

screwdriver in the slot beside each rivet to first ease out the rivet head and then fully remove
the rivet body. Separate the case halves. Visit www.tti-test.com for further details.

3) Remove the 3 screws securing the pcb to the case lower and lift out the pcb with front and rear
panels attached.

4) Change the voltage settings by changing the soldered links as shown below:

Installation

5) Reassemble in the reverse order.

6) To comply with safety standard requirements the operating voltage marked on the rear panel
must be changed to clearly show the new voltage setting.

Note: The transformer primary is protected by an integral thermal fuse which remains unchanged
when the operating voltage is altered.

Mains Lead

When a three core mains lead with bare ends is provided it should be connected as follows:-

WARNING! THIS INSTRUMENT MUST BE EARTHED WHEN OPERATED FROM AN AC LINE SUPPLY

Any interruption of the mains earth conductor inside or outside the instrument will make the
instrument dangerous. Intentional interruption is prohibited. The protective action must not be
negated by the use of an extension cord without a protective conductor.

Brown - Mains Live

Blue - Mains Neutral

Green / Yellow - Mains Earth

9

This section is a general introduction to the features and organisation of the multimeter intended
to be read before using the instrument for the first time. Detailed operation is covered in the
Making Measurements section.

Connections

Input Sockets

The input sockets are 4mm safety sockets on a 19mm pitch designed to accept 4mm safety plugs
with fixed or retractable shrouds. The sockets are all rated to 1000V (Category I)/600V (Category
II) with respect to earth ground.

The input impedance between V/Ω and COM is nominally 10MΩ. The black COM socket is
considered less positive than the red socket.

The mA/10A current sockets are low impedance; the voltage burden between mA/10A and COM
at full scale is <500mV. The black COM socket is considered less positive than the white mA/10A
sockets.

Multimeter Test Leads

General Operation

RS232

The test leads supplied meet the requirements of IEC1010-2-031 and are rated to 1000V
Category III. Use only the test leads provided, or a set of similar performance, to ensure safe
operation. Alternative test leads should be rated to at least 1000V (Category I),
600V (Category II) and 10A current capability.

The RS232 interface permits remote control and data-logging to disk using optional Windows
software. The interface is fully opto-isolated from the measurement system; the host computer
provides power (via the DTR and RTS lines) to the TXD opto output and drives the RXD opto
input directly. The 9-way D-type on the meter must be connected to the 9-way D-type of the PC’s
serial port via a 9-way cable (all connections made); the PC is nulled out at the multimeter
interface as shown below:

Pin Name Description
1 DCD Linked to DTR
2 TXD Transmitted data from instrument
3 RXD Received data to instrument
4 DTR DTR from host PC must be set to +9V (logic 0)
5 GND Signal ground
6 DSR Linked to DTR
7 RTS RTS from host PC must be set to -9V (logic 1)
8 CTS Linked to RTS
9 GND Signal ground

Signal grounds are connected to instrument safety ground.
To ensure compliance with EMC legislation use only screened cable assemblies with screened

connectors when connecting to other equipment.

10

Switching On

Power Switch

The multimeter is switched on and off with alternate presses of the Operate key. This key only
switches the DC power to the measurement circuits; it does not switch the AC power which
means that the isolated RS232 circuit continues to be powered. Disconnect from the AC supply
by unplugging the mains cord from the back of the instrument or by switching off at the AC supply
outlet; make sure that the means of disconnection is readily accessible. Disconnect from the AC
supply when not in use.

Power-up Settings

At power-up using the Operate key the default action is to restore power-down settings; the
power-down settings are not retained if AC power is removed.

To restore the default settings (Volts, DC, Autorange) press SHIFT then Reset.
Turning the meter on at the AC supply whilst any key is held down initiates a buzzer and display

test (all segments and annunciators should be lit); when the key is released the revision of the
installed firmware is shown in the display as x.x. Pressing the Operate key switches on the meter
as normal.

Buzzer

A short beep is sounded whenever an invalid key is pressed, e.g. pressing Hz when an AC range
is not selected; such keystrokes are not accepted. The buzzer is also used to indicate a
resistance <10Ω in Continuity mode.

Keyboard

Selection of the primary function is made directly by pressing the appropriate keys e.g. V and DC
for DC Volts; the primary function is showing beside the key. The meter is switched between
autoranging and manual with alternate presses of the Auto/Man key; alternatively using the
arrowed up and down keys changes the range and sets manual ranging.

The further functions (Null, Hold, Min-Max etc.) are all selected by pressing SHIFT followed by
the appropriate key; the shifted function is shown in blue above the key. When SHIFT is pressed
the annunciators for all the shifted functions are lit; when the function is selected with the
appropriate key only the associated annunciator remains lit.

11

Scale Length

The scale length is always ± 40,000 counts, except AC ranges which are ± 4,000.

Function Selection

All functions are directly selected by pressing the appropriate function keys (e.g. V followed by
DC to set DC Volts). Changing function sets autorange when there is more than one range;
providing the appropriate function has been selected (e.g. Ω for resistance measurement) and the
parameter to be measured is within the range of the meter, a valid reading should always be
shown.

Making Measurements

The units and function are shown in the display (e.g.
to indicate autorange.

Continuity and Diode Test and selected by pressing SHIFT followed by the appropriate key. The
associated annunciator confirms the selection. Continuity sets the meter to the 4kΩ range and
buzzes for values below approximately 10Ω.

Range Selection

Selecting a new function always sets autorange to ensure an in-range reading is made with
maximum resolution whenever possible; the meter ranges up at 40,000 counts (4,000 on AC
ranges) and ranges down at 3,840 counts (V and Ω) or 255 counts (mA); AC ranges range down
at 384 counts and 25 counts respectively.

There are, however, situations when it is desirable to lock the range; for example, to stop the
meter autoranging to the 40MΩ range and back between successive resistance measurements of
lower resistance values, or to set a lower resolution range when an unstable parameter is being
monitored. To lock the range, change from auto to manual ranging, see below.

Manual range changing is selected either by alternate presses of the Auto/Man key, which locks
the meter in its present range, or by using the arrowed up/down keys which both change the
range and lock the meter in that new range. The Auto annunciator is off in Manual mode.
Overrange is indicated by OFL in the display; overrange is shown when the count exceeds
40,000 in a manually locked range (1024V/768V on the 1000VDC/750VAC ranges respectively).
Autoranging can be restored by pressing the Auto/Man key again.

and V for DC Volts) together with Auto

Making Voltage Measurements

Voltage measurements are made using the red V/Ω socket and the black COM socket having
selected the appropriate function and range as described above.

The meter will show a minus sign (on dc measurements) when the voltage applied to the red
socket is more negative than that applied to the black socket.

Note that when AC voltage ranges are selected with the meter inputs open circuit a non-zero
reading will usually show because stray AC signals couple into the meter’s high impedance input.
This is perfectly normal and will not affect the accuracy of practical voltage measurements where
source impedance is generally low.

The maximum voltage that can be applied between V/Ω and COM is 1000V DC or 750V AC
(265V DC/AC rms on 400mV range), Category I; damage to the instrument may result if this limit
is exceeded.

WARNING! The maximum input voltage to ground must not exceed 1000V (Category I) or 600V
(Category II) dc or ac rms. Safety will be impaired if these ratings are exceeded, see Safety
section at the beginning of the manual.

12

Making Current Measurements

Having selected the appropriate current function (mA for 4mA and 400mA range, A for 10A
range), current measurements up to 400mA are made using the white mA socket and the black
COM socket; current measurements up to 10A are made using the 10A and COM socket. The
meter will show a minus sign (on dc measurements) when the polarity of the current is out of the
mA or 10A sockets.

Current measurements using the mA socket can be autoranged between the 4mA and 400mA
ranges; measurements up to 10A can be made using the 10A socket having selected the 10A
range with the A key.

The 4mA and 400mA ranges, using the mA socket, are protected by a 1A (F) HBC fuse and the
10A range, using the 10A socket, is protected by a 10A (F) HBC fuse. Both fuses are fitted inside
the instrument and replacement is described in the Maintenance section later in the manual.

Note: After measuring high current using the 10A input, thermal voltages are generated that may
create errors when making measurements on the most sensitive dc voltage, current or Ohms
ranges immediately afterwards. To ensure that the specified accuracy is maintained, allow 10
minutes for the thermal effects to fade before making sensitive measurements.

Making Resistance Measurements

Resistance measurements are made using the V/Ω and COM sockets.
Null can be used to null out residual test lead resistance, see Further Functions section.

Making Continuity and Diode Checks

Continuity and diode checks are made using the V/Ω and COM sockets.
Select Continuity mode by pressing SHIFT followed by Continuity; the continuity indicator is

shown in the display. The 4kΩ range is selected and readings below approximately 10Ω sound
the continuity buzzer.

Select Diode Test by pressing SHIFT followed by Diode Test; the diode annunciator is shown in
the display. The 4V range is selected and the diode voltage at approximately 1mA is shown
(3V maximum). Reverse diode connection will show overload (OFL).

Making Frequency Measurements

Frequency measurements are made using either the V/Ω and COM sockets (for AC voltages) or
mA/10A and COM (for AC currents).

First set the input sensitivity by selecting the appropriate AC volts or current range to give an in­range measurement of at least 2,000 counts; then press the Hz key to select frequency mode.
Two ranges (4kHz and 40kHz) are available giving resolutions of .1Hz and 1Hz respectively over
an operating frequency range of 10Hz to 40kHz.

The default frequency range is 40kHz which has a 1s gate time. To select the 4kHz range (10s
gate time) use the arrowed down key; the Hz annunciator flashes slowly to indicate that the 4kHz
range has been selected. The 40kHz range can be reselected with the arrowed up key.

At low signal levels use a screened lead and an adaptor (BNC to 4mm plugs, 19mm pitch) to
preserve signal quality and avoid spurious readings from stray pick-up.

Note that the further functions of Null, Hold, T-Hold and Min-Max (next section) do not operate
with frequency measurement.

13

Null

Hold

Further Functions

The further functions of Null, Hold, T-Hold and Min-Max are all selected by pressing SHIFT
followed by the appropriate key; the shifted function is shown in blue above the key.

Selecting Null stores the current reading and subtracts it from all the following readings. The
meter range is locked and Null shows in the display. Hold, T-Hold and Min-Max can all be
subsequently selected but changing function or range (or selecting Auto) will automatically cancel
Null. Null can also be cancelled by pressing SHIFT followed by Null.

Null can be used to null out the effect of residual test lead resistance on the lower Ohms ranges.
Select the appropriate Ohms range using the arrowed up/down keys. Connect the test leads
together, wait for the reading to settle and select Null. Make the Ohms measurements in the usual
way but note that if Auto is reselected or if the range is changed then Null will be cancelled. Null
cannot be used with Hz.

Selecting Hold freezes the reading in the display and flashes the Hold annunciator. Hold can be
used with the Null already selected but Null and Min-Max cannot be selected once Hold is set.
Selecting any other function (including range change, Auto/Man and T-Hold) will set that function
and cancel Hold. Hold cannot be used with Hz.

T-Hold

In T-Hold (Touch and Hold) mode the meter will hold a reading until a new non-zero measurement
has been detected; this allows the user to touch-probe the measurement point, remove the
probes and read the meter afterwards. Care should be taken, however, when using T-Hold with
the most sensitive voltage ranges; when the probes are lifted from the circuit being measured
their high impedance means that stray pick-up might generate another ‘valid’ reading and the true
T-Hold reading may be lost. Selecting T-Hold locks the meter range and shows the T-Hold
annunciator in the display. When T-Hold is initially selected it is automatically ‘armed’ and the first
valid (non-zero) reading will cause the display to update with a beep and the T-Hold annunciator
to flash.

The meter will re-arm (2 beeps) when it subsequently sees a near-zero reading (because, for
example, the probes have been removed from the measurement) but the original reading is held
in the display. After the 2 beeps the T-Hold annunciator stops flashing to confirm that the meter is
armed and a new reading is taken when the probes next make a non-zero measurement. With
Ohms and continuity measurements, overflow, associated with the probes being open-circuit, re­arms the meter. For all functions a measurement change of more than 1000 counts will also
initiate a re-arm/new measurement cycle. T-Hold can be used with Null already selected but Null
and Min-Max cannot be selected once T-Hold is set. Selecting any other function (including range
change, Auto and Hold) will set that function and cancel T-Hold.
T-Hold cannot be used with Hz.

Min-Max

While Min-Max is selected the minimum (most negative) and maximum (most positive) readings
are stored. The Min and Max readings can be displayed, while Min-Max is running, by using the
Review function (SHIFT followed by Review). The first SHIFT/Review displays the Minimum,
indicated by flashing the Min annunciator; the second SHIFT/Review displays the Maximum (Max
flashes); the third SHIFT/Review returns the display to normal with Min-Max still running.

Min-Max can be turned off by pressing SHIFT/Min-Max again. Selecting another function or range
or Auto also cancels Min-Max. Null, Hold and T-Hold cannot be selected with Min-Max running.
Min-max cannot be used with Hz. Review cannot be used with Min-Max turned off.

14

Routine maintenance is limited to re-calibration and cleaning. The only repair maintenance that
can be carried out by the user is current range fuse replacement.

Calibration

Calibration is guaranteed as in the specification. The manufacturers provide a re-calibration
service, as do most of their agents overseas. Where owners wish to carry out re-calibration
themselves, this should only be done by skilled personnel with access to precision equipment
working in conjunction with the service manual which may be purchased directly from the
manufacturers or their agents overseas.

Current Range Fuses

The mA socket is protected by a 1A (F) HBC fuse and the 10A socket by a 10A (F) HBC fuse,
both mounted internally. To replace a fuse, proceed as follows:

1. Disconnect the instrument from all voltage sources.

2. Unclip the front bezel by gently pulling the centre of each long edge up and forward.

The case halves are held together by 4 plastic push-rivets. Use the blade of a small
screwdriver in the slot beside each rivet to first ease out the rivet head and then fully
remove the rivet body. Separate the case halves. Visit www.tti-test.com for further
details.

Maintenance & Calibration

3. Replace the fuse with one of an identical rating using the diagram below as a guide.

4. Reassemble in the reverse order.

Mains Fuse

The transformer primary is protected by an integral thermal fuse which is not user replaceable.
Should a fault develop which causes the thermal fuse to blow, the meter must be returned to the
manufacturer or agent for service.

Remote Operation

The RS232 interface permits remote control and data-logging to disk using optional Windows
software; operation is controlled by clicking with the mouse on the keys of the virtual front panel
displayed on the PC.

Connection between the RS232 port and the PC’s serial port is made using a 9-way D-type to
D-type cable with all connections made, see Connections section under General Operation.

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