Greetings all,
I'm considering purchasing a RevPi connect and an IO module for an energy project. The most immediate need is for an input to take 200ms DC pulses and count them. Obviously a DI or DIO module would make the most sense for this, but I may need 4-20mA input and output in the future. Is it possible to use the RevPi AIOs inputs and set thresholds to sense and count pulses?
Pulse counting with RevPi AIO module
Re: Pulse counting with RevPi AIO module
Hi, you need an AIO if you want to measure currents. There is no "counter" feature available in the AIO module.
You have to implement according to your needs. So according to the Nyquist theorem you have to use the double sampling rate for it: 100ms.
Have a look at the "Spec sheet RevPi AIO"
The Input conversion time is adjustable from 8...1000 ms. So this will work.
You idea about thresholds is right, there is no threshold feature available on the AIO module.
But if so you would also need a hysteresis.
At the end we also have to remember that there is a cycle time that you have to measure on your system to know how
fast the process image will be updated.
So so sum it up to answer your question I need more details about your application.
Which components do you need? Just a RevPi Core and an AIO module?
You have to implement according to your needs. So according to the Nyquist theorem you have to use the double sampling rate for it: 100ms.
Have a look at the "Spec sheet RevPi AIO"
The Input conversion time is adjustable from 8...1000 ms. So this will work.
You idea about thresholds is right, there is no threshold feature available on the AIO module.
But if so you would also need a hysteresis.
At the end we also have to remember that there is a cycle time that you have to measure on your system to know how
fast the process image will be updated.
So so sum it up to answer your question I need more details about your application.
Which components do you need? Just a RevPi Core and an AIO module?
Re: Pulse counting with RevPi AIO module
Thanks for the reply Dirk.
So the project is an industrial CHP unit operating on MWM's TPEM control system. This unit has been manufactured to our specification and a gas flow meter and kalorimeter inputs wired in. While the TPEM system will take the pulses from those two instruments, it doesn't have the ability to do anything more with those pulses than count them. Then it can pass that total count value out over MODBUS RTU on RS485. This isn't overly useful to us as the maintainers of the CHPs, I'd like to get better data. Those pulses actually represent either a specific volume of gas per pulse or a number of BTUs per pulse. I'd like to create something that gives a current rate of those values or a 6, 12, or 24 hour average of those values. This is why the RevPi is appealing.
My goals with RevPi on this system are as follows:
- Bring in MODBUS RTU on RS-485 and convert to BACNET or AB PLC (RevPi connect and node red?)
- Bring in the pulse signals from the gas flow meter and kalorimeter. These can be as high as 24 vdc, but I can configure a voltage divider if needed. Pulse lengths can be short, 50ms or so.
- Allow for future expansion of binary/digital inputs and industry standard PLC 4-20mA input and output
I wish there was a single module that had 1 or 2 of each DI, DO, AI, and AO.
So the project is an industrial CHP unit operating on MWM's TPEM control system. This unit has been manufactured to our specification and a gas flow meter and kalorimeter inputs wired in. While the TPEM system will take the pulses from those two instruments, it doesn't have the ability to do anything more with those pulses than count them. Then it can pass that total count value out over MODBUS RTU on RS485. This isn't overly useful to us as the maintainers of the CHPs, I'd like to get better data. Those pulses actually represent either a specific volume of gas per pulse or a number of BTUs per pulse. I'd like to create something that gives a current rate of those values or a 6, 12, or 24 hour average of those values. This is why the RevPi is appealing.
My goals with RevPi on this system are as follows:
- Bring in MODBUS RTU on RS-485 and convert to BACNET or AB PLC (RevPi connect and node red?)
- Bring in the pulse signals from the gas flow meter and kalorimeter. These can be as high as 24 vdc, but I can configure a voltage divider if needed. Pulse lengths can be short, 50ms or so.
- Allow for future expansion of binary/digital inputs and industry standard PLC 4-20mA input and output
I wish there was a single module that had 1 or 2 of each DI, DO, AI, and AO.
