Heat-Prober (700M); General Discussion - Wahl Heat-Prober 392AHP User Manual

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Heat-Prober Platinum-RTD Thermometers User Manual
13.0 700M THERMISTOR .01°C/F RESOLUTION HEAT-PROBER

13.1 General Discussion

The Wahl Thermistor unit measures temperature over a range of -1.00°C to 60.99°C (30.20°F to
141.78°F) with .01°C resolution. The sensing element in the probes is a highly stable thermistor,
with .1°C interchangeability, the out- put being processed and linearized before display. The
accuracy of the meter is .02°C. With probe installed, the accuracy is .04°C.
The signal conditioning circuitry is completely chopper stabilized and associated resistive
components have a very low temperature coefficient. This combination yields essentially drift
free operation.
The linearization of the Thermistor sensor is accomplished in two steps for best utilization of the
available analog-to-digital converter range. A resistive network accomplishes a portion of the
linearization while a look-up" table in the microprocessor completes the balance.
All operations of the instrument are controlled by the microprocessor including the drive for the
display and peak reading computation and retention. Another important feature of the
instrument is the use of dual power regulators and dual grounding systems to provide the
ultimate in isolation between sensitive signal conditioning circuits and the high level digital
processing and display circuits.
The power source of the 700M is the same as the 392M, which is a recharge- able nickel-
cadmium battery pack composed of five AA size cells with a combined voltage of 6.0 volts and
capacity rating of .65 amp-hours. The unit is supplied with a recharger which can be plugged in
at any time to maintain the charge of the battery pack. Low battery condition is displayed as "L"
in the left-hand side of the display. The 700M is available only with LED display.
Should the temperature being measured extend beyond the limits of the instrument, or in the
event the probe is removed from the unit or becomes defective and opens, an indication of -OL-
will be displayed on the LED dis- play. Correcting the over/under range condition or inserting a
functioning probe will again bring the instrument to a proper indicating condition.
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