turbine/rotor flow sensor

[otrotabi]

I would like to use a turbine/rotor type flow sensor. It consists of a magnet which is mounted on top of the rotor and a Hall effect sensor placed on top of the rotor.

The model I am looking will generate a square wave output signal with a frequency (hz) = 6 x flow (lts/min) and a maximum flow of 50 lts/min, so that should give us a maximum 300 hz square wave input.

I could use either TM171 (preferably) of TM172 if needed.

I have done something similar in the past with the help of @LeTomas. What we did  was to input the rotor flow directly to an analog input and hopefully the RC characteristics of the input gives a dc value which is related to the input frequency/flow.

So basically my question is: is there a different approach I could use ? Could I count pulses with a Rtrig for example ? I guess not because 1/300 = 3.3 msec which is far less than 100 msec scan time but I am a little lost.

[FedericoM · Accepted solution]

The right solution should be the 24Vdc fast digital input of TM172, it counts pulses and provide frequency of the last period.

What you did in the past with M171 might work also in this case, but I guess with a lower accuracy,

If you want just to detect if there are pulses or not (flow alarm), SmartBios lib allows to read DI status both on background and timed, combining this with a debounce reduced to 0 on the DI. If this is the case M171 could be enough...

[otrotabi]

I will probably end up using a TM172 (or eventually a dedicated square wave to dc board should I need to use TM171) but you have made me curious and I would like to learn something new 🙄.

I guess the SmartAsyncDI is the FB you refer to.

What does it mean that it runs asynchronous from timed task ? Where should I place this FB ? 

In any case, go/no go is not what I am looking for (particularly because you may get a 1 if there´s no flow in case the magnet is placed under the hall effect sensor) but also since I would like to stop the chiller if flow gets below a certain flow. In any case I am not trying to implement a good flowmeter here.

I would also be willing to try other suggestions if I can get away from paddle switches which are hard to set up correctly.

[Bastian_Schmitz]

Which typ of Flow switch did you use? The turbin sensors from SIKA with NPN output work proper an DI1 or DI2. But in that case you need to connect the NPN output to COM_DI of CN3 and 24V+ constant signal on DI1 or DI2. In that case you lost one Digital Input.

[Bastian_Schmitz]

Or you could use a Vortx sensor with analog output like these Link

[otrotabi]

I am afraid I do not get them here from Sika, at least not from stock. Looks like a fine solution. I will try to find out if there are any distributors.

This is what I get here. I´ve tried a similar plastic case version and they work fine for a long time (or until they break, whatever happens first 😁). Seriously, they seem to work. Probably Sika has included an op amp and some other stuff to count pulses and give you a DC output with the same principle. We are trying to get away from paddle type switches.