Control options for compressors with single phase & 3 phase AC electric motors.

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The most common pressure transducers use a current-loop. It's an industry standard that has been in use for decades.
The transducer can be connected with a very long wire (half a mile is no problem at all). A fault can be detected easily: 0mA or no current means a disconnected transducer or an error condition while 4mA means a reading of zero.

These transducers are neatly priced, accurate and I have been using them for over 2 years without a glitch. A 60MPa transducer has a range that is too large - better options are 25MPa, 30MPa or 40MPa, depending on the maximum pressure that you want to measure.

How does it work?
First you need a power source, anything from 12V to 36V DC will do. The transducer is connected to the power source and will send a current. Most electronics can't do much with a current, so it's translated to a voltage (which is what the transducer mentioned by @Rol diy does). That voltage can then be sent to a analog/digital converter that a processor can use.

Texas Instruments created a tiny little chip that does all of that, the INA226:

ina226currentloop.jpg

The current loop runs from the positive terminal of the DC power supply over a resistor (0.1 Ohm / 1% precision), then to the transducer and finally back to the ground terminal of the power supply.
The chip measures the voltage difference over the precision resistor and translates that into a 16-bit value, which is from 0 to 65535.
That value is sent over the I2C bus (SDA/SCL pins) to an arduino / raspberry / esp32 / other computer.

Measuring the output pressure of the compressor with a 40MPa transducer (400bar / 5800psi) gives a value of 13107 for zero pressure and 65535 for max pressure. That's over 52000 steps for 5800psi - enough precision for an accurate reading.
Measuring the pressure of bank(s) is a matter of adding more of these chips (up to 16) and transducers, the same power supply can be used for all of them.
 
The most common pressure transducers use a current-loop. It's an industry standard that has been in use for decades.
The transducer can be connected with a very long wire (half a mile is no problem at all). A fault can be detected easily: 0mA or no current means a disconnected transducer or an error condition while 4mA means a reading of zero.

These transducers are neatly priced, accurate and I have been using them for over 2 years without a glitch. A 60MPa transducer has a range that is too large - better options are 25MPa, 30MPa or 40MPa, depending on the maximum pressure that you want to measure.

How does it work?
First you need a power source, anything from 12V to 36V DC will do. The transducer is connected to the power source and will send a current. Most electronics can't do much with a current, so it's translated to a voltage (which is what the transducer mentioned by @Rol diy does). That voltage can then be sent to a analog/digital converter that a processor can use.

Texas Instruments created a tiny little chip that does all of that, the INA226:

View attachment 712586
The current loop runs from the positive terminal of the DC power supply over a resistor (0.1 Ohm / 1% precision), then to the transducer and finally back to the ground terminal of the power supply.
The chip measures the voltage difference over the precision resistor and translates that into a 16-bit value, which is from 0 to 65535.
That value is sent over the I2C bus (SDA/SCL pins) to an arduino / raspberry / esp32 / other computer.

Measuring the output pressure of the compressor with a 40MPa transducer (400bar / 5800psi) gives a value of 13107 for zero pressure and 65535 for max pressure. That's over 52000 steps for 5800psi - enough precision for an accurate reading.
Measuring the pressure of bank(s) is a matter of adding more of these chips (up to 16) and transducers, the same power supply can be used for all of them.

Thanks for the details.
Is there a way to use this to run say a relay or a ssr? I am not that smart in knowing what electronic components are needed, one day I want to understand how to use arduino / raspberry.

The 0-10v seems like it's not an accurate way to go, if using it for high pressures,

Your first link helped me alot thanks
 
Yes:
Connect the INA226 chip(s) to the i2c bus of an arduino. Once the arduino reads a value that corresponds with the shut-off pressure, it can change a 5V relay from close to open. The other side of that small relay is part of the loop that switches the main relay for the compressor motor - if that loop is interrupted, the compressor will stop. That's how I did my initial design to control my compressor.
 
Thanks for the details.
Is there a way to use this to run say a relay or a ssr?
The 0-10v seems like it's not an accurate way to go, if using it for high pressures

It's very accurate, but it's not terribly precise depending on what level of stop pressure you want. If you want it to stop at 4500psi on the nose it's the wrong application but if you are OK within 50psi it's fine *which is about 1%, so that's pretty bloody tight*. They read in hundredths of volts typically so they're quite accurate but the reality is that a ~5F temperature swing is worth about 1% of pressure swing so there isn't much value in being more precise than that.

If you want one to run a relay you have two choices. First and easiest one is to use a pressure switch instead of a pressure transducer where the output is going to switch the relay directly. The other is to start to make a basic PLC using arduino's, raspberry pi's, or commercial solutions and then you can scale up and add in whatever you want for sensors to shut the thing off.

If you were building a brand new compressor it typically has the following
VFD-motor control if in Europe, most in the US are just starter relays
hall effect-rpm
Temp/Pressure for each stage
ACD relay
CO sensor
If you have a nitrox stick you can tie a solenoid to cut the O2 flow off when the pump is off, add a pressure switch off of the supply bottle to cut the pump off when the supply bottle is drained, and/or the O2 sensor to do whatever you want if the ppO2 is out of whack. If VFD equipped you could change the rpm of the pump, could shut it off, if you got fancy with servos you could open or close the needle valves, etc.
You can get crazy fancy with these things if you go hog wild.
 
Thanks I really need to learn arduino,
I know I could use it in my job,
I tend to be a more mechanical or electric person,

The link I sent had a digital pressure gauge built in (whichi liked), and seems that it can be set to certain pressures to control a relay,
it would be nice and compact and simple,,, not so sure the output is as simple as I thought

C$ 51.70 | pressure transmitter with LCD Display G1/4 12-36V 0-10V 0.5% 0-600bar optional stainless steel pressure transducer sensor
 

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