PhotoHelic Differential Air Pressure Sensor to Rack Power Safety System (RPSS) Box --------------------------------------------- Rev. 30-NOV-1994 This adapter box will receive the signal from the PhotoHelic differential air pressure sensor that monitors the difference in air pressure between M100 and M113 and convert this signal into one that can been feed into an Air Flow input on the RPSS box. This adapter box is made from a water flow sensor adapter box. Layout of the PhotoHelic Differential Air Pressure Sensor --------------------------------------------------------- PhotoHelic Differential Air Pressure Sensor B A Layout of pins from the rear view of the C H F AMP Hex connectoron the PhotoHelic gauge D E Connections: Upper Limit Switch: E,F Lower Limit Switch: C,D Bulb: A,B no connection H When cold the bulb has about 4.8 Ohms resistance. It may operate at very low power, i.e. mostly as an IR emiter, for long life. The detectors are photo resistors. When pulled out of their narrow slot holders they look like 2k in room light and >100k in the dark. When in their narrow slot holders they look like 120k in room light and 20k to a flashlight held at about 1 foot distance. When the PhotoHelic is all put back together, exposed to room light and the limit sensor positioned so that it is outside of its limit range, then the detector has > 10 meg Ohms of resistance. The detectors are part No. CL905L 421. The Lower Limit detector is dark until the pressure is > the lower limit. The Upper Limit detector becomes dark when the pressure is > the upper limit. Sensor Resistance Lamp Current Lamp Volts when exposed to the lamp ------------ ---------- ------------------------ 50 mA 1.19 Volts 730 k Ohms 55 1.43 440 k 60 1.69 230 k 65 1.96 130 k 70 2.25 81 k The cable resistance from the RPSS box to the PhotoHelic-RPSS Adapter and back is about 1.47 Ohms. At 65 mA this results in a total voltage drop of 96 mV. Thus if we want to run the bulb at about 65 mA we will need a resistor that gives a voltage drop of (5.0 Volts - 1.96 Volts - .096 Volts) when there is a 65 mA current through it ---> 45.3 Ohms perhaps at 40 Ohm fixed plus a 10 Ohm variable. Dissipation will be about 200 mW in this dropping resistor. 3Volt 2.2k up --+ Ref 3.3k down | 5 +-------------+ 2 +-------------+ +---- inverting | Ref 2.5 Volts ------- inverting | | input | 7 15k up 15k down | input | 200k to +5 | Output -----> | output ------------------------ non-invert | to 900k up to +5 | | 1 0.1 mFd to 6 | input | RPSS Photo Sensor to ---- non-invert | signal common +-------------+ signal common 3 | input | +-------------+ Cable from PhotoHelic to the PhotoHelic_to_RPSS Box Cable PhotoHelic PhotoHelic-RPSS Color Pin Number Box Pin Number Function ------- ---------- --------------- ----------------------- Red A 1 Bulb Power positive Black B 9 Bulb Power return White C 4 Photo Sensor signal Green D 12 Photo Sensor return In the PhotoHelic to RPSS Adapter Box the following connections are made on the connector that goes to the cable that runs to the RPSS: Pin #1 Air Flow Sense LM393 output pin #7 Pin #9 Air Flow Sense ground signal common in PhotoHelic to RPSS Adapter Box. Pin #3 Vcc +5 Volt to operate the PhotoHelic to RPSS Adapter Box and the PhotoHelic bulb. Pin #11 Signal Common power return in PhotoHelic to RPSS Adapter Box. Pin #2 Temperature Sense jumpered to Pin #10 Temperature ground Pin #4 Water Flow sense jumpered to Pin #12 Water Flow ground Pin #6 Water Pressure sense jumpered to Pin #14 Water Pressure ground Pin #7 Spare sensor sense jumpered to Pin #15 Spare sensor ground Pins #5, #8, #13 open Standard for all RPSS Rack Sensor Input Connections Cable Connections to RPSS for Rack Sensor Cables (J1 thru J13) -------------------------------------------------------------------- PIN COLOR SENSE LINE NAME PIN COLOR GROUND LINE NAME --- ----- ----------------- --- ----- ------------------ 1 black Air Flow sense 9 white Air Flow ground 2 red Temperature sense 10 purple Temperature ground 3 pink Vcc to flow sensor 11 tan power return flow sensor 4 blue Water Flow sense 12 brown Water Flow ground 5 n.c. 13 n.c. 6 green Water Pressure sense 14 yellow Water Pressure ground 7 gray Spare sensor sense 15 orange Spare sensor ground 8 n.c.