Probes; Interchangeability - Wahl Heat-Prober 392AHP User Manual

Heat-Prober

3.0 PROBES

Probes compatible with the 392 Heat-Prober are constructed utilizing a wire wound Platinum
RTD sensor with an R0 of 100 Ohms wired in a 3-wire con- figuration to compensate for lead
length effects. To provide probe inter- changeability at 0 degrees C, a balancing resistor is
added to the sensor circuit and trimmed for a total resistance of 100.94 Ohms at 0°C. (See
Figure 3-2)
The High Performance Heat-Prober, Model 392HP, utilizes probes similar to the 392 but
incorporating an additional calibration resistor that provides probe interchangeability at all
temperatures.

3.1 Interchangeability

Probes are individually balanced to 100.94 Ohms at 0°C to compensate for variations in
different probe configurations. This guarantees probe interchangeability at 0°C. In addition, each
probe is tested at a minimum of one higher temperature. This calibration data is recorded on a
calibration tag attached to the probe. (See Figure 3-1)
Probe Interchangeability (Immersion)
Ice Point ±0.3°C (±0.5°F)—(392HP ±0.2°F)
100°C ±0.6°C (+1.0°F)
200°C ±1.1°C (±2.0°F)
Surface probes are tested on surface calibration plates especially built to replicate the end-use.
The variance is somewhat larger as follows:
100°C ±1.1°C (±2.0°F)
200°C ±2.2°C (±4.0°F)
Figure 3-2. Probe Circuit NOTE: Platinum sensor element manufacturers quote 0.1% tolerance
at 0°C, or 0.1 ohms on a 100 ohm sensor. This results in 0.3°C variance. The tolerance at higher
temperatures is greater than 0.1% in accordance with the following formula as specified by DIN
43760: Tolerance = ±.3°C + .0054t (°C)
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Platinum-RTD Thermometers User Manual
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