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1908
User guide
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Table of contents
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Aim TTi 1908, 1908P User guide

1908
5½ Digit Dual Measurement Multimeter
CONTENTS
1 Product Description ......................................................................................................4
2 Safety .............................................................................................................................5
Symbols ...............................................................................................................................6
3 Installation .....................................................................................................................7
4 Getting Started ..............................................................................................................9
4.4.1 On/Off operation with AC Power .............................................................................9
4.4.2 On/Off operation without AC Power ......................................................................10
4.4.3 Power-up Settings.................................................................................................10
5 Measurement Connections ........................................................................................ 10
5.1.1 Multimet er Test Leads ..........................................................................................11
5.2.1 Trigger In/Out ........................................................................................................11
5.2.2 Digital Interfaces ...................................................................................................11
5.2.3 AC Inlet .................................................................................................................11
5.2.4 Protective Earth Terminal .....................................................................................11
6 Making Basic Measurements ..................................................................................... 12
6.6.1 Two Wire Measurements ......................................................................................13
6.6.2 Four Wire Measurements .....................................................................................14
6.7.1 Continuity Measurem ent .......................................................................................14
6.7.2 Diode Checks .......................................................................................................14
7 Additional Parameters and Functions ....................................................................... 16
Page 1
7.4 Temperature Measurement (oC/oF) ........................................................................ 17
8 Dual Measurement Mode ............................................................................................ 18
9 Triggered Operation .................................................................................................... 20
10 Advanced and Programmable Functions .............................................................. 21
11 Data Logging ............................................................................................................ 23
12 The Utilities Menu .................................................................................................... 25
13 Maintenance ............................................................................................................. 27
13.1.1 Zero Calibration ....................................................................................................27
13.1.2 Routine Calibration ...............................................................................................27
13.3.1 Current Range Fuses ............................................................................................27
13.3.2 Internal AC power fuse .........................................................................................28
13.5 Firmware Updates ............................................................................................... 28
Page 2
14 Remote Operation .................................................................................................... 29
14.4.1 LAN IP Address and Hostname ............................................................................31
14.4.2 mDNS and DNS-SD Support ................................................................................31
14.4.3 ICMP Ping Server .................................................................................................31
14.4.4 Web Server and Configuration P as sword Protection ............................................31
14.4.5 LAN Identify ..........................................................................................................31
14.4.6 LXI Discovery Tool ................................................................................................32
14.4.7 VXI-11 Discovery Protocol ....................................................................................32
14.4.8 VISA Resource Name ...........................................................................................32
14.4.9 XML Identification Docu ment URL ........................................................................32
14.4.10 TCP Sockets .....................................................................................................32
15 Status Reporting ...................................................................................................... 32
15.1.1 Input Trip Register (ITR) .......................................................................................33
16 Remote Commands ................................................................................................. 37
16.1.1 Remote and Local Operation ................................................................................37
16.1.2 Remote Command Handling .................................................................................37
16.1.3 Remote Command Formats ..................................................................................37
16.1.4 Command Timing..................................................................................................38
16.1.5 Response Formats................................................................................................38
16.2.1 General Commands ..............................................................................................39
16.2.2 Main Display Commands ......................................................................................40
16.2.3 Dual Measurement Mode Commands...................................................................42
16.2.4 First Level Modifier Commands ............................................................................42
16.2.5 Second Level Modifier Commands .......................................................................43
16.2.6 Data Logging Commands .....................................................................................44
16.2.7 Common Commands ............................................................................................45
16.2.8 Status Commands ................................................................................................45
16.2.9 Interface Management Commands .......................................................................46
17 Default Settings........................................................................................................ 47
18 Graphical Interface PC software ............................................................................. 48
19 Specifications .......................................................................................................... 49
Note: This manual is 48581-1470 Issue 3
Page 3

1 Product Description

This precision bench-top/portable multimeter has dual measurement capability and a dual display which can show either two independent measur ements, a measurement together with its range value, or a measurement with one of the many programmable functions available.
The key features are:
• Operation from AC line or built-in rechargeable batteries.
• 0.02% basic accuracy, 120,000 counts.
• Manual or Auto-ranging.
• DC and AC Volts, DC and AC current, Resistance, Capacitance, Frequency, and
Temperature measurement; Continuity and Diode checks.
• True RMS AC and AC+DC measurement.
• Two or Four wire selectable ohms measurement.
• Display nulling and Ohms null.
• Selectable measurement speed.
• Touch hold mode - holds onto a stable reading until updated.
• 500 point data logger with timer.
• Temperature measurement for PT100 or PT1000 sensors.
• Measurement post-processing to give:
dB and power measurement with settable reference impedances percentage deviation from a user-entered reference linear scaling with offset limits comparison for go/no go testing automatic storage of minimum and maximum readings.
• Remote control via USB interface (1908)
• Remote control via USB, RS232, GPIB and LAN (LXI) interfaces (1908P)
• External input/output remote triggering.
• 1908-PC Link software providing:
Remote control of main functions Logging function with graphical & tabular displays Logged data can be exported to a CSV file
• Closed case calibration.
• Fully compliant with EN61010-1, EN61010-2-030 & EN61010-2-033 Safety, and
EN61326-1 EMC standards.
Page 4

2 Safety

This multimeter has been designed to meet the requirements of EN61010-1, EN61010-2-030 & EN61010-2-033 (relevant parts of the ‘Safety Requirements for Electrical Equipment for Measurement, Control and Laboratory Use’ standards). It can be operated from its built-in rechargeable battery or from a standard AC mains supply (Overvoltage Category II). When connected to AC mains, it is a Safety Class I instrument.
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.
When operated from the internal battery, without an AC mains connection, the multimeter should be earthed by connecting the rear panel Chassis Earth terminal to an external protective earth system. Without this connection, ‘leakage’ current from any accessible part may exceed the Normal (s afe) limit of 0.5mArms under some extreme measurement conditions, e.g. high voltage, high frequency, AC volts measurement. Measurements to 300VACrms, 50/60Hz, for example, would not require this protective earth connection.
The test leads supplied with this instrument meet the requirements of EN61010-031 and are rated to 1000V Cat 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 2 environment (only dry non-conductive pollution occurs except that occasionally a temporary conductivity caused by condensation is expected) in the temperature range 5°C to 40°C, 20% - 80% RH (non-condensing). It may occasionally be subjected to temperatures between +5° and −10°C without degradation of its safety.
It has been designed for measurement use to 1000VDC/750VACrms in circuits isolated from AC mains power (derived secondary circuits within an equipment) with occasional transient over­voltages up to 1500Vpeak. It can also be used for CAT II (Measurement Category II) use to 600VDC/ACrms, and CAT III use to 300V DC/ACrms. CAT II is local domestic supply level, e.g. portable equipment and appliances; CAT III is mains distribution parts of a building.
For this equipment 4000V 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, including the replacement of the current range protection fuses. 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 sof t dry cloth to clean the display window.
Page 5

Symbols

CAUTION - refer to accompanyi ng
Measurement Category I I. Inputs may be
alternating current
Measurement Category I II. Inputs may be
The following symbols are used on the instrument and in this manual:
WARNING - risk of electric shock.
documentation; incorrect operation may damage the meter.
CAT II
connected to AC mains power under Category II overvoltage conditions
CAT III
connected to AC mains power under Category III overvoltag e conditions
mains earth (ground)
Protective Earth terminal
direct current
Standby supply. Instrument is not disconnected fr om AC mains power when switch is off.
Page 6

3 Installation

3.1 Mains Operating Voltage

Check that the instrument operating voltage marked on the r ear panel is suitable for the loc al supply. Should it be necessary to change the operating voltage, proceed as follows:
1. Warning! Disconnect the instrument from all voltage sources before beginning this
procedure.
2. Pull out both sides of the handle at the case pivot points, to fr ee the position locking pegs, and rotate the handle from the stowed position to the position shown below. Then pull the sides of the handle outwards fully, one at a time, to remove the handle completely.
3. Remove the two screws on the rear panel that retain the top cover and slide the top
cover towards the rear, with the soft bezel still in place, until it can be lif ted clear.
Note: To avoid contaminating or damaging the PCB assembly, take care not to touch
any components other than the two shorting connectors described in the next step.
4. Remove the shorting connector in position PJ4 on the PCB beside the mains
transformer (TX1) and replace it with the alternative shorting connector from the ‘parking’ position PJ8; align pin1 of the connector with the pin 1 corner marker of the header. ‘Park’ the unused connector on PJ8, see the diagrams below.
For 230V operation PJ4 should be fitted with the connector which has a single red wire between its centre pins (pins 2 & 3). For 115V operation PJ4 should be fitted with the connector which has a blue wire between pins 1 & 3, and a brown wire between pins 2 & 4. Note that the value of fuse FS3 (500mA) is the same for both AC voltage settings, see Maintenance, section 13.
5. Reassemble in the reverse order.
6. To comply with safety standard requirements the operating voltage marked on t he rear
panel must be changed to clearly show the new voltage setting.
Page 7

3.2 Mains Lead

For AC mains operation, connect the instrument to the AC supply using the mains lead provided. Should a power plug be required for a different power outlet socket, a suitably rated and approved mains lead set should be used which is fitted with the required wall plug and an IEC60320 C13 connector for the instrument end. To determine the minimum current rating of the lead-set for the intended AC supply, refer to the power rating information on the equipment or in the Specification.
WARNING! THIS INSTRUMENT MUST BE EARTHED.
Any interruption of the power earth conductor inside or outside the instrument will make the instrument dangerous. Intentional interruption is prohibited.

3.3 Mounting

This instrument is suitable both for bench use and rack mounting. It is delivered with soft protective front and rear bezels which have integral moulded feet; this is the most suitable configuration for bench use.
For rack mounting the protective bezels and handle/stand can be removed such that the instrument can be fitted beside any other standard 2U half-rack instrument in a 19” rack. A suitable 2U 19” rack kit is available from the Manufacturers or their overseas agents; full details of how to remove the handle and bezels are included with the kit.

3.4 Handle/stand

The instrument is fitted with a 4-position handle/stand. Pull out both sides of the handle at the case pivot points, to free the position locking pegs, and rotate the handle from the stowed pos it ion to the required stand or handle position. Release the sides of the handle to lock it in the new position.
Page 8

4 Getting Started

4.1 Using this Manual

In this manual front panel k eys are shown in bold square brackets , e.g. [Vdc], [Function]. Sockets are shown in bold capitals, e.g. INPUT HI. LCD display dat a is show in bold curly brackets, e.g. {SPEEd}, {AUTO}.
The manual is available in pr i nted form and as an electronic document in PDF format. The manual includes cross r eferences which are underlined within the text. These are hyperlinks within the PDF document . The Table of Contents is also fully h yperlinked.
Hyperlinks enable the u s er to jump rapidly to the section referred to and then jump back to continue reading the original section. (N.B. f or hyper l ink navigation within Acrobat Reader, enable “show all page navigat ion tools” or use the keyboard shortcuts Alt+Left_Arrow and Alt+Right_Arrow).

4.2 Installation and Safety

Before first use, all user s should read the Safety Information in section 2 . Before connecting AC power, c hec k that the instrument operating voltage marked on the rear
panel is suitable for t he local supply. Should a change be required, read section 3.1 Connect the instrum ent to the AC supply using the mains lead provided. Should a power plug
be required for a different power outlet socket, refer to section 3.2
.

4.3 AC Power and Battery Operation

The instrument can be operat ed from AC power or from internal rechargeable batteries which are recharged as required when AC power is connected. A red LED is illuminated whenever AC power is connected and a yellow LED is illuminated whilst c harging is taking place.
Battery Life from fully charged is approximately 20 hours with the backlight on, and up to 35 hours with the backlight off. Under battery operation a battery symbol will appear on the display if the charge level falls belo w about 10%. The approximat e charge level can be checked from the Utilities menu – see section 12.5.
For the 1908P, operation of the remote interfaces (excludi ng USB) is only possible with AC power connected.

4.4 Switching On and Off

The instrument behaves differently depending upon whether or not AC power is connected.
4.4.1 On/Off operation with AC Power
If required, AC power can be switched on or off using the POWER switch mounted on the rear panel. When the AC power is switched off the default setting is for the instrument to turn off. Th i s ensures appropriate behaviour when used as part of a group of equipment for which AC power is turned on or off simultaneously.
Note: To fully disconnect from the AC supply unplug the mains cord from the back of the instrument or switch 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.
The green front panel button marked [OPERATE] can be used to place the instrument into Standby if required. Successive presses will alternate between On and Standby.
Alternative AC Power Swi tching Options
The response of the instrument to AC power being connected or disc onnected can be altered if required. The actions described above are the default conditions, and can be changed fr om the Utilities menu – see section 12.9
.
Page 9
4.4.2 On/Off operation without AC Power
Display
Measurement Measurement keys
Navigation
Function keys
Power
Function keys
With no AC power connected, operation is from the internal r ec hargeable batteries and the instrument is turned on or off by successive presses of t he green [OPERATE] button. The rear panel POWER switch has no funct i on.
4.4.3 Power-up Settings
At power up the display briefly shows the installed software revision; the instrument is then restored to the same measurement conditions as at power down, including any advanced functions that were running. However, if the instrument was showing a menu at power down, the menu will be cancelled when powered up.

5 Measurement Connections

5.1 Input Sockets

keys
The input sockets are 4mm safety sockets on a 19mm pitch designed t o accept 4mm safety plugs with fixed or retra ctable shrouds. All sockets are rated to 1000Vpeak with res pec t to earth ground. Safety will be maintained if voltages up to 1000Vpe ak are accidentally applied between inappropriate terminals in excess of their marked ratings, but restoration of normal operation may require replacement of protection devices (e.g. cur rent range fuses).
terminals
The input impedance between INPUT HI and INPUT LO is nominally 10MΩ on dc r anges and 1MΩ on ac ranges. The black LO soc k et is considered less positive than the red socket. The maximum voltage that can be app lied between HI & LO is 1000Vdc, 750Vrms (1000Vpeak). The sockets are rated to 600V CAT II, 300V CAT III.
The mA/10A current sockets are low impedance; the voltage burden between mA/10A and LO at full scale is <100mV for the 10mA range and <600mV for the 100mA, 1A and 10A ranges. The black LO socket is considered less pos itive than the white mA/10A sockets. The mA/1A socket is protected with a 1.6A 1kV HRC fuse, and the 10A socket with a 10A 1kV fuse; see Maintenance, section 1 4, for replacement details.
The SENSE HI & LO sockets are only used in 4-wire Ohms and RTD temperature measurements; refer to those sections for details. When used, the maximum differential between SENSE LO and INPUT LO should be < 0.5V peak . The SENSE terminals are protected against accidental connection of up to 200Vpeak between HI & LO.
Page 10
5.1.1 Multimeter Test Leads
The test leads supplied meet the requirements of IEC1010-031 and are rated to 1000V Cat
TTL/CMOS External Trigger
Kensington
USB
RS232
LAN
Power switch
AC power
Protective
(1908P)
GPIB
III. Use only the test leads pr ovided, or a set of similar performance, to ensure safe operation. Alternativ e test leads should be rated to at least 1000V, 600V (Cat II) and 10A current capability.

5.2 Rear Panel Connections

connection
(1908P
only)
Conductor
Terminal
Warning! This instrument must be
earthed. Connect terminal to an external protective earth system when instrument is used without an AC mains connection.
Lock
5.2.1 Trigger In/Out
Screw-less connectors are provide d on the rear panel for the connec tion of an external trigger signal, and a trigger out s ignal . See section 9
for full details.
5.2.2 Digital Interfaces
Depending upon model, r ear panel connectors are provided for USB only (1908) or USB, RS232, LAN and GPIB (1908P). Refer to Remote Operation, section 14
, for full details.
5.2.3 AC Inlet
The instrument can be connected to AC mains using the power lead supplied or a suitable alternative, see Installation section 3.2.
When the power lead is connected this lead provides the
necessary protective earth connection to an external protective earth system.
5.2.4 Protective Earth Terminal
For battery only operation, without an AC power lead connected, the M4 threaded chassis connection marked must be connected to an external protective earth system via a
green/yellow insulated cable, with a cross-section of at least 0.75mm Without this connection, ‘leakage’ current from any accessible part may exceed 0.5mArms, t he Normal (safe) limit specified by EN61010-1, under some extreme measurement conditions, e.g. high voltage, high frequency, AC volts measurement.
. WARNING! THIS INSTRUMENT MUST BE EARTHED.
2
, fitted with a M4 terminal.
Page 11

6 Making Basic Measurements

Primary measurement
Range or
Functions
Remote
Status
Range
This section describes how basic measurements are made, i.e. single measurement mode without post-processing of the results.

6.1 Scale Length

The scale length is ±120,000 f or all measurements except frequency (full scale 12,000) and capacitance (full scale 1200). {OFL} is displayed when the range maximum is exceeded.
Note, however, that safety considerations limit the maximum voltage and current that can be measured to below the scale length maximum.

6.2 Measurement Parameter Selection

Refer to the f r ont panel diagram in section 5.1 The two rows of darker grey keys below the display directly select t he measurement parameters for either the primary or secondary display. When pressed alone the param eter keys select the measurement parameter for the primary display, cancel any secondar y functions, and set the range to auto-range.
Pressing [2nd] followed by a parameter key selects the parameter for the secondary display; this is explained fully in Dual Measurement Mode, section 8 combinations of parameters that can be used.
Additional paramet ers marked in blue above certain keys are selected by first pressing [SHIFT]. Whilst shift is operational a {SHIFT} symbol appears on the left side of the display. See section 7
for full details.
, which also details the

6.3 Measurement Range Selection

Refer to the front panel diagram in section 5.1, and to the display diagram below.
communications
2nd measurement
When a parameter is first selected, auto-ranging is enabled and a n {AUTO} s ymbol is displayed. Pressing either of the [ᴧ] / [v] arrow keys (Range+/Range-) cancels auto-ranging whilst leaving the range set to its existing value. The {MAN} symbol is displayed and further presses then change the range up wards or downwards. Pressing [OK] returns the ins trument to auto-ranging operation.
The units appropriate to the function and range (e.g. {mV ac}) ar e s hown to the right of the display. When the secondary display is not being used to sho w m easurement values, the selected range is shown there.
Note that the 10A range, which uses a different input socket from mA measurements, can only be selected manually. Once 10A has been selected, however, this setting will be retained for current measurem ent unt il i t is returned to mA.
Note that the {AUTO} and {MAN} symbols apply only to the pr imary display.
Mode
Page 12

6.4 Making Voltage Measu rements

The maximum voltage that can be applied between INPUT HI and LO is 1000V DC or 750V
The input test leads and AC power lead must be disconnected before opening the fuse
Having selected Vdc or Vac, volt age measurements are made us ing the red INPUT HI socket and the black INPUT LO socket within the yello w area of the panel. Five measurement ranges (auto or manual) are available from 100mV to 1000V (dc) or 750V (ac).
The meter will show a minus sign {-} (on dc measurements) when the volt age applied to the INPUT HI socket is more negative than that applied to the INPUT LO socket.
AC; damage to the instrument may result if this limit is exceeded.
WARNING! The maximum input volt age to ground must not exceed 1000V peak. Safety will be impaired if thes e ratings are exceeded, see Safety section at the beginning of the manual.

6.5 Making Current Measu rements

Having selected Idc or Iac , current measurements up to 1. 2A (1200.00mA) are made using the white mA socket and the black INPUT LO socket; cur rent measurements up to 10A are made using the 10A and LO sockets. The meter will show a minus sign {-} (on dc measurements) when the polarity of the cur r ent is such that it flows out of the mA or 10A sockets rather than into it.
Using the mA socket three measurement ranges ( auto or manual) are available f r om 10mA to 1000mA. Measurements up to 10A c an be made using the 10A socket having manually ranged to 10A with [ᴧ].
The 10mA, 100mA and 1000mA ranges, using the mA socket, are protect ed by a 1.6A (F) HRC fuse. The 10A range, using the 10A socket, is protected by a 10A (F) HRC fuse. Both fuses are accessed via a panel on the bas e of the instrument.
access panel.
Note: After measuring high currents (i.e. above half sc ale) using the 1A or 10A ranges, thermal voltages are generated t hat may create errors when making measurements on the most sensitive dc voltage, current or Ohms ranges immediat el y afterwards. To ensure that t he specified accuracy is maintained, allow 10 minutes for the thermal effects to reduce before making sensitive meas ur ements.

6.6 Making Resistance Measurements

Pressing [Ω 2/4] selects resistance measurement in either 2 wire or 4 wire mode. Successive presses alternate between the modes as indicated by {2W secondary display. Six measurement ranges (auto or manual) ar e available from 100Ω to 10MΩ.
6.6.1 Two Wire Measurements
Normal (2 wire) resistanc e measurements are made using the INPUT HI and LO sockets within the yellow area of the panel. This measurement mode is appropriate for higher r es istance measurements, and for lower res istance measurement s where high precision is not required.
Ω} or {4WΩ} appearing briefly in the
The effects of test lead resis tance can be removed using Ω Null if required – see section 7.3
Page 13
.
6.6.2 Four Wire Measurements
4 wire measurements are appropr iate for precision measur ement of low resistances where the effects of the connectin g l eads and contact resistances are significant. 4 wire measurement uses the HI and LO SENSE sockets in addition to the HI and LO INPUT sockets. Connections are made as shown below.
Two Wire Measurement Four Wire Measurement
Because no significant current is flowing through the SE NS E connections when utilising 4 wire measurement, contact resistance does not affect the measurement result.

6.7 Making Continuity and Diode Checks

Pressing [ ] selects either cont inuity measurement or diode test. Successive presses alternate between the two as indicated by symbols on the left side of the displ ay. Continuity and diode checks are made using the INPUT HI and LO sockets within the yellow area of the panel.
6.7.1 Continuity Measurement
Setting continuity causes the 1000Ω range to be selected such that readings be low approximately 10Ω will sound the continuity buzzer. Readings above the range maximum will
show {OPEn}.
6.7.2 Diode Checks
Setting diode check caus es the 1000mV range to be selected and a current of approximately 1mA to flow out of the INPUT HI socket. W ith the anode of the diode connected to this t erminal the diode forward voltage will be shown. Reverse diode connecti on will show {OFL}.

6.8 Making Frequency Measurements

Pressing [Hz] selects frequency m eas urement. Measurements are m ade using the INPUT HI and LO sockets within the yellow area of the panel. Four ranges (100Hz to 100k Hz) are available, giving resol utions of 10mHz to 10Hz respectively over an operating fr equenc y range of <10Hz to 120kHz. Reciprocal counting techniques ensure fast reading updates (4 readings/second) even on the lowest range. This can be increased to 8 readings/second in fast speed mode see section 12.2 measuring low frequencies in the 100Hz range to ensure accurat e r eadings.
; however the slow speed mode should always be used when
Measurements are m ade using the ac Volts input circuitry which is auto-ranged to provide suitable sensitivity. At low signal levels use a screened lead an d an adaptor (BNC to 4mm plugs, 19mm pitch) to preserv e signal quality and avoid spurious r eadings from stray pick-up. The minimum measurable signal is <30mV rms across the frequency range (100mV range) or <10% of range maximum for other ac voltage and current ranges.
Frequency can also be meas ur ed in dual measurement mode, see section 8.1
Page 14
.

6.9 Making Capacitance Measurements

Pressing [ ] selects capacitance measurement. Measurements are made using the INPUT HI and LO sockets within the yello w area of the panel. Five ranges ( 10nF to 100µF) are available with 1200 count full scale giving resolutions of 10pF to 100nF respectively.
Zero calibration at the factory is carried out with no test leads c onnected; ideally, capacitor s to be measured should be connected directly to the sockets. Test leads, if used, should be kept as short as possible to minimise stray capacitance but never theless a non-zero reading will generally be present when the lowest ranges are selected. To eliminate this offset it is recommended that the meter reading is nulled, once the required range has been selected, with the test leads in their measurement positions but no capacit or connected.
It is also recommended that battery operation is used when making capacitance measurements, to m inim i s e reading jitter. Note that, becaus e the capacitor is discharged between each measurem ent, the reading rate on the 100µF range is slower.

6.10 Over Voltage Protection

When making measurements of Resistance, Capacitance, Temperature, Continuity or Diode checks an internal protection circuit protects t he current source from source voltages applied to the INPUT HI and LO sockets. If a voltage of greater than typically 10V is applied to the INPUT HI and LO sockets the protection circ ui t will be engaged, the buzzer will sound and {trIP} will be displayed. After completion of the trip event, the measurement mode is set to V dc to show the over-voltage that is bein g appl ied to the input sockets. BIT 0 of the Input Trip Register (IT R) is set to 1 (over voltage protec t) see section 15.1
.

6.11 Measurement Hold

Hold operates only on the primary display. Pressing [Hold] causes t he measurement to be frozen on the display along with a {HOLD} symbol. Provided that the meter is not in dual measurement mode and not measuring capacitance, t he normal, updated, reading will be shown in the secondary display.
Hold only operates on the primary display, any measurement being shown on the secondary display will continue to updat e normally.
Hold is cancelled by pres s i ng [Hold] again, or by changing range or function.

6.12 Measurement Null

Null operates only on the primary display. Pressing [Null] causes the measurement to be stored and subtracted f rom all future readings. Pressing [Null] locks the meter in the selected range and shows {NULL} (and {MAN}) symbols. Provided that the meter is not in dual measurement mode and not measuring capacitance, t he normal, un-nulled, reading will be shown in the secondary display.
Null is cancel by pressing [Null] again, or by changing range or function.

6.13 The Cancel Key

[Cancel] can be used to return t he meter to a basic measurement mode. It cancels dual measurement mode, dB, N ull, Hold and T-Hold, and any programmable functions including the Logger. It does not cancel Ω Null.
Consequently [Cancel] should not be used to cancel a single function, such as Hold, if other functions need to be maintained.
Page 15

7 Additional Parameters and Functions

A number of additional capabilities can be accessed using the measurement parameter keys, as described below. Further functions also can be selected from the Functions menu key – see
section 10.1

7.1 Combined AC + DC Mea surements

Vdc+Vac or Idc+Iac measurements are made by pressing both keys t ogether. The reading displayed is the RMS sum √(dc
Both ac and dc measurements are made on the same range: the instrument will auto-range to a range which gives an in-range reading for both the ac and dc component of the parameter. Clearresult to be shown as an in-range reading.
2
+ ac2) and ac+dc is shown on the displa y.
Note that this is a special case of Dual Measurement mode (see section 8.3 measurement update rate is slowed accordingly.
) and the

7.2 Decibel Measurement (dB)

dB (deciBel) can be selected only when Vac is already in the main display. Pressing [Shift] followed by [Vac] shows the dB value of the Vac measurement (referred to the chosen impedance setting) and dis plays the {dB} symbol. If no secondary f unc tion is selected the normal reading in volts will be s hown in the secondary displa y.
dBs are shown in a fixed format with 0.1dB resolution, whatever r ange the Vac measurement is being made on. The value displayed is in dBm and is calculated from the formula:
dB = 10 log10 (1000 x V2/R), where R is the selected reference impedance.
The default reference impedance is 600Ω but a different value can be selected within the Utilities menu. Press [Utilities], use the Navigator keys to select {rEF} and confirm with [OK]. The existing reference v alue will flash. Alternativ e val ues can be selected using the Navigator keys and confirmed with [OK].
Available values are 50, 75, 93, 110, 124, 125, 135, 150, 250, 300, 500, 600, 900, 1000, 1200, and 8000Ω. Pressing [Shift] followed b y [Auto] (Clear is the shifted function of Auto) returns the value to 600Ω. Press [Utilities] again to exit the Utilities menu.
dB is cancelled by pressing [Vac], or by selecting any other measur ement parameter or function.
7.3 Removing Test Lead Resistance (Ω Null)
Residual test lead resistanc e c an be nulled out using the Ohms Null facility as follows: Connect the test leads together and press [Shift] followed by [Ω 2/4] (Ω Null is the shifted
function of Ω). The 100Ω range is set automatically and the {NULL} symbol flashes; the meter stores the reading that it detects after 5 seconds provided that it is less than 1.000Ω (1000 counts). A beep sounds when the null is completed and the display should show zero Ohms and no {NULL} symbol.
If the reading cannot be nulled, because the offset is too lar ge, the reading will not change and the buzzer will not sound.
The Ohms null is stored as a floating point value which is used on all ra nges; it is not lost when the function is changed or when the ins trument is turned off. Ohms null can be cancelled by selecting Ohms Null and not generating a sub 1.000Ω reading within t he next 5 seconds, or by restoring the instrument to factory defaults – see section 12.8
Normal Null can be used together with Ohms Null.
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