Heat-Prober
®
Platinum-RTD Thermometers User Manual
16
6.3 Low Battery Adjustment and Testing
1. Connect DVM (-) to CR1 Cathode and (+) to upper side of R24.
2. Adjust R37 clockwise or counterclockwise until DVM reads 2.11 volts.
3. Disconnect DVM.
4. DISCONNECT BATTERY PACK. Low Battery indicator must be per- formed with an
external variable power supply. Start with 6 volts and slowly decrease the voltage toward 5.8
volts.
When the battery threshold is reached, a small “L”, or
“
←
”,
should appear in the most significant
digit posit
ion of the 392HP, 392E and 392M display. “Lo Bat” appears in the display of the
392EX, 392MX, 392EVX and 392MVX. The actual value of the low battery voltage threshold
may vary from 5.45 volts to 5.55 volts.
Keep decreasing the supply voltage until 5.5 volts is reached, as measured with a digital DVM.
The meter should maintain correct operation even though the small “L”,
“
←
”,
or “Lo Bat” is on,
indicating a low battery.
Now raise the voltage back up until the small “L”,
“
←
”,
or “Lo Bat” turns off. The voltage at which
this happens should be from 5.50 to 5.55 volts.
Under normal operation, an additional 20 minutes will elapse from the time the small “L”,
“
←
”,
or
“Lo Bat” appears until the battery voltage decreases to 5.5 volts, assuming a normal 5-pack of
AA NiCad batteries is being used. Below5.5 volts, the computer may introduce some errors or
not operate the display at all.
6.4 Zero Adjustment Using Wahl Calibrator
1. Insert the Wahl calibrator and adjust the calibrator to the 32°F/0°C position. Apply
power to the meter and make an initial adjustment at R5 for a reading of 32.0°F or 0.0°C
depending on your model.
NOTE: For the version 392HP, which has a 4-wire probe configuration, the microprocessor
averaging process is slightly slower. The moving average for the 392HP may be made faster by
turning the power off and then back on again, any time an input resistance or pot setting is
changed.
2. Make the best adjustment you can at this point, and then proceed to the span
adjustment.
