i got my hands on an ‘industrial standard’ hydrostatic level sensor (pressure sensor) from work that i plan to install in our rainwater tank but i need some help with identifying the wires. There is a data sheet on the manufacturer website but it does not tell me much about the wiring. I plan on using it with the shelly uni so i think i only need 3 (red, blue, white) wires. The sensor has 8 wires.
- gray (not black)
- breathing tube
I guess there is some color standard?
Also, the pressure sensor has an operating range from 15v to 28v. I guess i can use a 19v laptop charger? ) The shelly can use 12v to 36v.
I’m new to this kind of stuff so i hope someone can steer me in the right direction?
The data sheet lists the output wiring for each model. In all cases it is red, black and possibly white (if it is a 3 wire model).
There are 6 possible output types. E, Q, U, J, F or V.
Which model sensor do you have (what is the part number printed on it)?
Well, i know i have the 4mA~20mA DC version. (E22).
But i’m confused about the red and black wire. It says:
BK: +V and RD: +OUT printed on the sensor itself
Red: +V and BK: +OUT in the datasheet
If BK is ‘black’ and RD is ‘red’ then one of them is wrong. On top of that, there is no black wire at all. Only a grey one.
We also know this sensor is modified by another company so there is a possibility that this is a 3 wire model but RED (V+), BLUE (V-), WHITE (DATA)
I cannot find a serial number other than ‘MPM426W E22’ so…
The E version is 4-20mA. So 2-wire.
I think we can safely assume that grey is black. If you know the sensor has been modified I’d be inclined to believe the label on the device rather than the datasheet.
Red to load resistor
Black/grey to +V (though this does seem odd to me, perhaps you should ask about the modifications).
Load resistor to ground.
Measure output across the load resistor.
There’s an equation in the data sheet for calculating the load resistor, it must be less than or equal to:
(V - 15) / 0.02 Ohms.
E.g. for your 19V supply:
(19 - 15) / 0.02 = 200 Ohms.
The closer you get to this value the larger your output voltage swing will be. You are looking at 0.8v to 4v for 4 to 20mA. Which is only a third of the Shelly Uni’s 12V ADC input. So not a good choice.
Id be inclined to use an ESP32 which has a programmable input range.
Yeah, red is +V. We cut the cable before the plastic ‘breather thingy’ and as it turns out only the red and black cables are connected to the green and yellow one’s… Why, i do not know. But now we know we have a 2 wire variant so i think the sticker on the sensor is wrong. Red is +, black is -.
I also ordered a 24v 125mA powersupply. I’ll post the wiring diagram and some pictures when i have the time.
This is the wiring diagram we came up with. This is ok i think? I don’t have the resistor yet so i can’t test it.
The original cable has actually 5-wires: red, black, white, green and blue.
I used two 1000Ohm load resistors in parallel but the ADC voltage reads 0v all the time. Even with the sensor submerged.
I get 466Ohm when using a multimeter.
Which is still higher than the maximum 450 Ohms allowed for your 24V supply.
I realized that, but even with 3x1000Ohm (measured 329Ohm) it sits at 0v. We also tried 4x100Ohm (measured 411Ohm) in serie but got the same result.
What does a multimeter measure across the sense resistor?