MVD ancillary - the level sensor


The level sensor is a LV171 from Omega. It takes 12V, and has a signal line which switches from +3.5V to 0 when the sensor tip gets wet.
I use a SN74SC04N hex inverter chip to invert this, and a solid state relay (opto 22 model 240D45-17 switches the 110V AC of the drain valve. The unused inputs of the chip are tied to ground (via >100K resistors), and a 680 Ohm resistor brings down the 12V to under 8V for the chip power. Total current is 22 mA at 12V.





postscript version <--

Parts list
part need (for 3 units) have
connector, 10-pin 0.1" mini 3 3
connector, 3-pin 3 3
socket, 14-pin 3 0
chip, SN74HC04N 3 1
R, >100K, 1/8W 15 0
Zener, TRW 4627 3 2
relay,3V -> 110V~ 3 3
.


  A MIL-D9 connector on the heat exchange/fan assembly combines signals and power for the humidity sensor, drain valve and the motor DC power. The pin assignments at the heat exchanger box are as in the table below. On the rack end, the cable is split three ways into the humidity sensor 10-pin connector, the level sensor 10-pin connector and the motor power.

pin group function
1 humidity sensor +12 V
2 humidity sensor gnd
3 humidity sensor signal
4 fan control variable voltage
5 fan control return
6 level sensor +12 V
7 level sensor gnd
8 level sensor signal
9 - nc

Last update 6 July 2000 - HvH
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