392Hp And 392M Options - Wahl Heat-Prober 392AHP User Manual

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Heat-Prober Platinum-RTD Thermometers User Manual
8.0 392M and 392HP OPTIONS
8.1 392HP
The "HP" option allows probes to be calibrated and interchangeable over the entire temperature
range. This also results in superior system accuracies at all temperatures. The "HP" option
utilizes a Noise Rejection program which minimizes transient noise effects.
In this version a special 4-pin receptacle is installed at the probe connection, and the four pins
are wired to the printed circuit board from the probe connector side as shown in Figure 8-1. A
resistor with a nominal value of 5K is installed in each individual probe via the extra pin. 5K
resistance indicates to the microprocessor that nominal curve values in the memory shall be
used.
Other values of this resistor tell the microprocessor to initiate corrections to the nominal curve.
Close matching with a probe is achieved as follows: The probe is tested at a specific bath
temperature, and a decade box is attached where the R33 resistor would be in the probe. The
resistance is adjusted until the 392HP reads the precise temperature of the bath, for example
100°C, taking out the tolerance of the probe. A value of 4K, for example, may be needed in the
decade box to adjust the reading by 0.2%. The new resistor value of 4K tells the microprocessor
to make an adjustment for that specific probe. The decade box is removed, and a resistor with
the same value as the adjusted box is potted inside the 4-pin probe connector between pins 3
and 4 (See Figure 8- 2).
8.2 Degree F to C Conversion (Specify Suffix D)
The microprocessor provides true digital conversion for temperature throughout the whole range
of the instrument. This switch is a convenience where dual measurement scales are needed.
Each HP version probe, therefore, has its specific resistor to indicate to the microprocessor the
correction to be taken.
Figure 8-1. Wiring Diagram for 392HP
Figure 8-2. 4-Pin Probe Connector Expanded View
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