3000.doc Iss. 2/00
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ZERO This key zeros the displayed value and "Zero" appears in the bottom left hand corner
of the display. NOTE: The Zero offset will be cancelled if the measuring channel is
changed, if the calibration menu is entered, or if the sensor configuration is changed.
TRIG The TRIG key operates in two modes. These may be set using the OPT menu. The
default mode enables the TRIG key to be used as a run/hold button and Run appears
on the display above the key, pressing TRIG holds the display and Hold will appear
on the display. It will also be noticed that the flashing "Busy" blanks in the hold
mode. Pressing TRIG a second time returns the instrument to the run mode. The
second mode of operation may be set using the OPT menu. This enables the TRIG
key to be set in single shot mode, i.e. when pressing the TRIG key, one
measurement is made and held on the display, and the busy sign flashes once. It
should also be noted that even for large changes in temperature readings the new
measurement will be valid, the specially designed measurement circuit ensures that
the A/D converter is fully zeroed and stabilised before a new measurement is
displayed.
When used in conjunction with the data logging function the TRIG key is used to
start the logging. Pressing the TRIG key again puts the instrument into a hold state
and the measurement channels may now be changed. Restarting the measurement
by pressing the TRIG key also resumes the data logging; the newly selected
measurement channel now being stored. It is possible to store readings from
channels A, B, or A-B. When in single measurement mode the instrument is
normally in the hold state. Pressing the TRIG key initiates one measurement which
will be stored in the log , the instrument then returns to the hold state.
+I This selects the measuring current in the positive direction. The measuring time is
approx. 1.8 seconds per reading for channels A and B, and 3.6 seconds for A-B.
-I This selects the measuring current in the negative direction. Measuring time approx.
1.8 seconds per reading for channels A and B and 3.6 seconds for A-B.
AVE This automatically switches the measuring current from forward to reverse direction
and displays the average of the 2 readings thus eliminating any errors due to thermal
emf. Measuring time approximately 3.6 seconds per reading for channels A and B
and 7.2 seconds per reading for A-B
√2 Current is reduced through the measuring probes by √2 (half power) enabling any
probe self heating to be determined. The best method of use for this option is to first
allow the sensor to reach a steady temperature and note the value, it will take some
time for the sensor to stabilise. Select √2 current and immediately press the ZERO
key, the reduced current through the probe will reduce the heating effect on the probe
and any value displayed will represent the temperature change due to the reduced
current. The advantages of using the ZERO key in this way are twofold, firstly, any
errors in the measuring amplifiers due to a change in current are removed, and
secondly from a calculation point of view, the change in reading will be displayed
without further calibration being required.
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