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7.4 Temperature Measurement (
o
C/
o
F)
The instrument incorporates linearised measurements for PT100 and PT1000 platinum
resistance temperature detectors (RTDs).
The temperature function is selected by pressing the shifted function marked °C/°F [Shift]
[]. The default measurement is in degrees centigrade. To change to degrees fahrenheit
select the function again.
The default probe type is PT100. To change to PT1000 use [<] / [>].
The measurement can use either a 2 wire or 4 wire connection, the latter using the HI and LO
SENSE terminals in addition to the HI and LO INPUT terminals. The selection is made from the
Utilities menu – see section 12.7
.
7.5 Touch and Hold (T Hold)
T-Hold causes the meter to “hold” a reading on the display 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. It is not available for Ohms, Continuity, or Diode Test
measurements.
T Hold is selected by the shifted key marked T-Hold [Shift] [Hold].The{T-HOLD} symbol is
displayed, and each new reading is indicated by a beep sound. Measurement update is slow,
and small changes to the signal that occur after the probes have been connected will not be
shown.
Note that care should be taken 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.
T-Hold operates only on the primary display in both manual and auto-range modes; it is
cancelled by pressing T-Hold again [Shift] [Hold] or by changing the measurement parameter
or range.
7.6 Measurement Speed and Measurement Filter
The normal measurement speed is 4 readings/sec for most single measurement parameters.
For voltage, current and resistance measurements, the speed can be increased to 20
readings/sec at the expense of resolution which reduces to 12,000 counts. This is done from
the Utilities menu, see section 12.2
.
In order to minimise jitter for sensitive measurements, an analogue filter is incorporated that
provides high rejection of 50Hz or 60Hz noise. Where the user requires quicker response to
signal changes, the filter can be switched off. This is particular relevant when the measurement
speed is set to 20 readings/sec. The filter is controlled from the Utilities menu, see section
12.3.
7.7 Zero Re-Calibration
An automatic zero calibration of the basic DC measurement circuitry is performed every time
that the instrument is switched on. However, if the meter has been stored at a temperature
outside the specified operating range, and is switched on before it has fully acclimatised to the
working environment, accuracy may be affected as the meter’s temperature changes. To
ensure optimum accuracy, particularly on the 100mV and mA current ranges, zero calibration
can be repeated when the meter has acclimatised by using the Null key as follows:
Press [Null] and continue to hold it down until {nULL} shows in the main display (about 3
seconds later). {nULL} continues to show whilst the auto-zero is being performed (typically 5
seconds); on completion the display returns to its previous mode.
Auto-zeroing in this way cancels Null if this was already selected; press [Null] again to re-select
if required.
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