Wahl 2500MX, Instruction Manual

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5.4.2 Span Adjustment with Millivolt Source
1) Insert copper wires into the thermocouple probe socket to apply the milli-
volt signal. A calibration temperature should be chosen so that it is at the
high end of the temperature range of the instrument (within about 10% of
the upper limit of the range). Look up this temperature that you have chosen
in the millivolt tables in the appendix of this manual for your thermocouple
type. Now, look up the millivolt value for the recorded room temperature.
Subtract the millivolt value equivalent to room temperature from the millivolt
value equivalent to your chosen calibration temperature. This calculated
value is the signal that must be applied to the Heat-Prober, adjust span
compensation with R22 so that the chosen calibration point appears on the
display. This will complete the span adjustment
Example: Type K thermocouple calibration point chosen is 1300°C (mV 52.398).
Room temperature = 25°C (mV = 1.000). The input signal is then 52.398 - 1.000 =
51.398mV. R22 is adjusted so that the display reads 1300°C with an input signal of
51.398mV.
NOTE: For Type S, the instrument has been programmed to read accurately between
55°F (13°C) and 95°F (35°C) and at 32°F (0°C) to accommodate these standard cali-
bration procedures, even though the stated range does not go below 200°F (90°C).