How can I connect a Hall Effect Flow Sensor Pulse output to PLC?

kunalv · Sep 30, 2019

Hey guys,

I am building a small prototype for a Coolant Dispensing System and need to measure the flow rate of water & chemical in the pipe in order to control the opening of valves downstream.

Since I am building a small pilot system, I can't really spend too much money and hence I intend to use those cheap Hall Effect Flow Sensors available online. Accuracy isn't important right now, but repeatability is!

So my question, how do I connect the Pulse Output of the Flow Sensor to the PLC?

JesperMP · Sep 30, 2019

When asking questions like that it is customary to post a link to the device in question.

kunalv · Sep 30, 2019

Apologies..

Here you go

JesperMP · Sep 30, 2019

It is for 5VDC.
You would normally use a signal conditioner 5VDC/24VDC to get the signal into the PLC.
A less expensive solution is to use a simple relay with 5VDC coil voltage.
You also need a power supply that outputs 5VDC.

kunalv · Sep 30, 2019

JesperMP said:
It is for 5VDC.
You would normally use a signal conditioner 5VDC/24VDC to get the signal into the PLC.
A less expensive solution is to use a simple relay with 5VDC coil voltage.
You also need a power supply that outputs 5VDC.

Thanks for the suggestion JesperMP.

So the Pulse output of the sensor goes to the 5VDC relay, output of which is fed to the PLC right? How do I configure the PLC to read this?

I'm sorry if this sounds stupid, as I honestly am not into Electronics. If you can draw a simple sketch, I'd be indebted to you! Thanks.

JesperMP · Sep 30, 2019

This is very basic, I dont have time for that.
I suggest you get assistance from someone who has some electrical knowledge.

gclshortt · Sep 30, 2019

https://accautomation.ca/wiring-interposing-relays/

The above post will help you with interposing relays.
Regards,

kallileo · Sep 30, 2019

As I see from the datasheet you have attached the sensor has supply voltage range 5 - 24V so you can directly connect it to a PLC input.
You cant use relays it this application.

bernie_carlton · Sep 30, 2019

Do you have the specifications on the PLC in question?

kunalv · Oct 1, 2019

JesperMP said:
It is for 5VDC.
You would normally use a signal conditioner 5VDC/24VDC to get the signal into the PLC.
A less expensive solution is to use a simple relay with 5VDC coil voltage.
You also need a power supply that outputs 5VDC.

kallileo said:
As I see from the datasheet you have attached the sensor has supply voltage range 5 - 24V so you can directly connect it to a PLC input.
You cant use relays it this application.

That's the problem, you know, since these are commercially available low-cost sensors (probably made in China), there is no authentic technical literature available other than what you find online.

I have been advised to use an Optocoupler with the sensor so as to scale the output from 5V to 24VDC and use a PLC with a high-speed counter card. Can someone verify this please?

JesperMP · Oct 1, 2019

Some counter cards accept 5 VDC signals directly, for exactly this reason.

kallileo · Oct 1, 2019

kunalv said:
That's the problem, you know, since these are commercially available low-cost sensors (probably made in China), there is no authentic technical literature available other than what you find online.

I have been advised to use an Optocoupler with the sensor so as to scale the output from 5V to 24VDC and use a PLC with a high-speed counter card. Can someone verify this please?

I have cheap Chinese flowmeters like you have and they worked with 24V but you have to be careful.
You can use an optocoupler, a mosfet or a transistor if you don't want to risk supply the flowmeter with 24VDC. Then you measure the frequency of the pulses to calculate the flow in L/min.

You can also use 5V input card a Jesper suggest.
What kind of PLC do you have?

It's possible that you will need a pull-up resistor as well.

kunalv · Oct 1, 2019

kallileo said:
I have cheap Chinese flowmeters like you have and they worked with 24V but you have to be careful.
You can use an optocoupler, a mosfet or a transistor if you don't want to risk supply the flowmeter with 24VDC. Then you measure the frequency of the pulses to calculate the flow in L/min.

You can also use 5V input card a Jesper suggest.
What kind of PLC do you have?

It's possible that you will need a pull-up resistor as well.

I haven't purchased a PLC yet mainly because I'm not sure which one to get for this application.

Could you tell me what is the need for the pull-up resistor? Is it to convert a 5V signal to 24V for the PLC? Doesn't the Optocoupler do just that?

parky · Oct 7, 2019

I have not used that particular unit but have used many others, as it say the unit will work from 5v to 24v so will interface with many PLC's. If you used a Mitsubishi FX range PLC the first 5 inputs are also high speed inputs up to I think 5khz so should be ok. See attached pdf file on how to use the high speed inputs on this PLC.
Note: only X0 used in this application and you must use the counter specifically tied to the input i.e. C235 > these are high speed counters and you do not need to reference X0-X5 as these are automatically assigned to the counters.

kallileo · Oct 7, 2019

kunalv said:
I haven't purchased a PLC yet mainly because I'm not sure which one to get for this application.

Could you tell me what is the need for the pull-up resistor? Is it to convert a 5V signal to 24V for the PLC? Doesn't the Optocoupler do just that?

I had used Schneider's Zelio SR3 smart relay but it should work with any PLC that has high speed input. Didn't use optocouplers or any other electonics besides pull-transistor.

Check the following article to understand more about flowmeters and pull-up resistors.
https://www.flowmeters.co.uk/flow-meter-output-selecting-optimum-output-flowmeter/

How can I connect a Hall Effect Flow Sensor Pulse output to PLC?

kunalv

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