Minco
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5
Power Supply
DC power supply requirements are determined by the humidity and temperature transmitter’s minimum
voltage requirement and voltage drop across the load resistor and installation lead wires.
Example: The transmitter requires 9.5 Volts minimum. A typical 250 ohm load resistor drops 5.0 Volts @ 20 mA.
Allowing a margin of 0.5 Volts for the supply permits 25 ohms of lead wire resistance for remote installation.
Totaling these, we get a minimum power supply requirement of 15.0 VDC.
Using a 24 VDC power supply will take care of nearly all installations, but the AH440 will operate at voltages up
to 35 VDC.
Humidity Transmitter Calibration
Calibration of the humidity transmitter can be done in a number of ways; comparison to another calibrated RH
instrument, using saturated salts, or in a controlled environment using a humidity chamber. The humidity and
temperature transmitters have non-interacting zero and span pots for field calibration.
Comparison method
To compare the calibration of the AH440 to another calibrated RH instrument, both sensors should be within
2” to 3” of each other with a fan blowing on both sensors for at least 10 minutes. This will equalize the
temperature of both sensors and emulsify the moisture content of the air. If adjustment is needed, adjust the
humidity zero (HZ) pot only. Refer to wiring diagrams 1-4 for location of the adjustment pots. Do not adjust
the span control.
Saturated Salts
Calibration is accomplished using saturated salt calibration cells as humidity standards. The cells are designed
for field use in constant temperature conditions. Various types of cells and their respective relative humidity
values are available. The cells must accept a 3/8” diameter probe. If adjustment is needed, and you’re
performing a single point calibration, adjust the humidity zero (HZ) pot only. For 2 point calibrations, use the
humidity zero (HZ) pot to adjust the low humidity calibration point and the humidity span (HS) pot to adjust
the high humidity calibration point.
Humidity Chamber
Follow the instructions of the humidity chamber for simulating humidity and temperature under controlled
conditions. If adjustment is needed, and you’re performing a single point calibration, adjust the humidity zero
(HZ) pot only. For 2 point calibrations, use the humidity zero (HZ) pot to adjust the low humidity calibration
point and the humidity span (HS) pot to adjust the high humidity calibration point. If the humidity span (HS)
pot is adjusted, go back and verify that unit is still within calibration at the low humidity calibration point.
Temperature Transmitter Calibration
Temperature Chamber/bath
Follow the instructions of the temperature chamber or bath simulating temperature under controlled
conditions. If adjustment is needed, and you’re performing a single point calibration, adjust the temperature
zero (TZ) pot only. For 2 point calibrations, use the temperature zero (TZ) pot to adjust the low temperature
calibration point and the temperature span (TS) pot to adjust the high Temperature calibration point. If the
temperature span (TS) pot is adjusted, go back and verify that unit is still within calibration at the low
temperature calibration point.