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I have a flow sensor that works with a 4-20 mA current loop. Is this compatible with OpenSprinkler? If it is not, is there a way to adapt a 4-20 mA signal to be compatible with OpenSprinkler?
Do you have a link to the flow sensor? Does it require constant current, or is it that it outputs current that’s proportional to the flow rate? If it’s the latter, there isn’t an easy way to make it work with OpenSprinkler — because in that case it’s outputting an analog signal, which needs to be fed into an analog pin. That requires changing the firmware to support such sensors. In contrast, the supported flow sensors work by sending pulses, and the frequency is proportional to the flow rate.
Hi Ray,
It is a Hunter flow sensor. I bought the sensor without the control module. Hunter does not seem to be to willing to share how their sensor works, but I did some experimenting and biased the two wires out of the sensor with various voltages and measured the current. As the paddle rotates the current changes from a low state (~4 mA) to a high state (~20 mA). Here are the actual measured results.
One way I thought of solving the problem is to drive a reed relay with the 4-20 mA current, that way I could isolate the sensor from OpenSprinkler and use a separate power supply to power the flow sensor. However I am having a bit of trouble converting the current to a usable voltage to drive the relay. I was wondering if this approach seemed reasonable or if there was an easier and more elegant way the community could suggest that I am overlooking. Unfortunately, the voltage across a 250 ohm resistor does not work since it converts the 4-20 mA to 1-5 VDC and the 1 VDC is above the threshold of the turnoff voltage of the relay. Maybe what I am really after is a circuit to convert 4-20 mA to 0-5V to drive the relay powered by a 12 or 24 volt power supply. I have a separate power supply that converts 24 VAC to 5,12 or 24 VDC.
I found an easy, inexpensive way to make the Hunter flow sensor compatible with opensprinkler, even though it may not be optimal. I found this board on the ebay:24V 4-20mA Current Detection Limit Value Control Switch Alarm Converter Module. The reason it is not optimal is that the relay should be a reed relay for reliability. I biased the sensor with 12 vdc with a separate 24vac to dc converter. I’ll attach a picture of the setup. I’m interested if anyone has a better approach.
Attachments:
I solved the reliability problem by removing the power relay from the board and soldered in a reed relay. Here is a link to the relay I used.
Overall I am satisfied with the hardware setup now. I like that the flow sensor uses a current loop for noise immunity. I also like that this setup isolates the flow sensor from the controller through the reed relay.
OK that’s good to hear, and thanks for the efforts to reverse engineer how this sensor works, and share your knowledge with us!
Could you please elaborate on how you are making that sensor work with OS? maybe a step by step? I have been trying to use data industrial or cst sensors unsuccessfully.
Thank you.
Could anyone help with this? I am really interested on getting a way to use either hunter, cst, or data industrial flow sensors.
Hi 951calguy,
I am not familiar with the cst or data industrial flow sensors. Could you possibly post a link or a datasheet? As far as the Hunter flow sensor there was not a lot of information out there about it so I had to run some tests to see how it exactly worked as I mentioned in a previous post. This would be the first step to try and figure out the interface of how it works and try and make it compatible with open sprinkler. In the end you need to interface you flow sensor to be compatible with the open sprinkler interface as described below.
Flow Sensor: when using a flow sensor, the controller will detect flow sensor pulses,
display real-time flow rate at the footer, and log the flow volume at the end of each
program run. Only dry-contact, 2-wire flow sensors are supported: these sensors are
essentially flow-activated switches which close and open repeatedly as water flows
through the meter. They do not need power, and typically come with 2 wires. Insert the
two wires to the sensor terminal on OpenSprinkler (there is no polarity). Then set the
flow pulse rate, which you can find out in your flow sensor’s datasheet, and is used to
convert the pulse count to actual volume. Flow sensors with 3 wires usually require
power and thus need some modifications before they can be used with OpenSprinklerIn order to make the Hunter flow sensor work you need three items.
1. The flow sensor itself.
2. Electronics that converts flow sensor interface to open sprinkler interface, open close contact
3. A power supply to drive the electronics in step 2.Maybe you can review the previous posts and ask more specific questions where you need help.
Hello Richard,
Here is the info I could get including some relay devices that may work with these type of flow sensor, I do understand that OS counts pulses but I don’t understand how the controllers that use these type of sensors have 2 ports where polarity does matter and there is actual dc voltage going to the sensor. Please check them and notice the 2 leads with color. Thank you I’m looking forward to your reply.
https://www.creativesensortechnology.com/
https://docs.wixstatic.com/ugd/956e06_0a161a52b48a4e27ba3c9e7eb76e13ad.pdf
https://www.badgermeter.com/brands/impellerdata-industrial/
http://www.netafimusa.com/landscape/products/water-meters/hydrometers/
After looking at the CST flow sensor, I am not sure how to interface to it. It looks like a two wire sensor where you bias the two leads with a power supply (8-35 VCD) and then they indicate the output is a voltage on the same two wires. It seems to make more sense to me that it would be a current and not a voltage, at least that is what I concluded with the Hunter flow sensor.
Do you own one of these sensors? If you do and have access to a voltage controlled power supply and an ammeter ad volt meter then you could run the same experiments that I did for the Hunter flow sensor to get a better idea of how it works. Or you could call them since they seem to be more open that Hunter at sharing information.
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