We have successfully had a system fielded for about a year now, and one of its several functions is to measure product flow through its channels. Given the application, chemical compatibility, cost, size and overall flexibility, I chose a Reed switch actuated flow meter and am sinking it into a National Instruments 9425 discrete input module, which is basically an I/O module for a PAC system called a cRIO 9068. I am using period-based calculations on the FPGA to derive a tick count and go from there, utilizing a known K-factor to calculate rate. The system is pretty accurate and has measured within manufacturer specified tolerance when compared to a Weights & Measures calibrated positive displacement flow meter that is far better.
Over time, especially recently, we have seen the flow meters get returned to us with tags describing two particular issues:
1.) Massive GPM rate (well beyond the range of the meter)
2.) No function
I recently tested a flow meter tagged "Broken, massive GPM" and replaced the side of the shell containing the Reed switch with a new one from the manufacturer. It worked correctly thereafter.
My question is... am I protecting my Reed switch well enough? Do I need some kind of debouncing circuit on the physical side to protect triggering and inherently filter it in the process? If so, I am not sure what those values for R1,R2 and C1 would be.
I don't drive inductive loads. I don't heat lamps. The length of cable (containing 22AWG 2 conductor) is, at most, 20 feet each way to the meter. This obviously isn't an A/C circuit. The 9425 has an input impedance of 30kOhms +/- 5% and I additionally supply a 1kOhm in series for good measure. This is a 12V power supply with a common ground. The flow meter manufacturer is very poor on communication, but has more or less stated this is fine. I question their tech support.
I assume the 10V (ON state requirement) / 30kOhm input impedance = how the minimum input current is derived? (330uA)
See attached image (apologies for the quality.)
Thank you all,
Over time, especially recently, we have seen the flow meters get returned to us with tags describing two particular issues:
1.) Massive GPM rate (well beyond the range of the meter)
2.) No function
I recently tested a flow meter tagged "Broken, massive GPM" and replaced the side of the shell containing the Reed switch with a new one from the manufacturer. It worked correctly thereafter.
My question is... am I protecting my Reed switch well enough? Do I need some kind of debouncing circuit on the physical side to protect triggering and inherently filter it in the process? If so, I am not sure what those values for R1,R2 and C1 would be.
I don't drive inductive loads. I don't heat lamps. The length of cable (containing 22AWG 2 conductor) is, at most, 20 feet each way to the meter. This obviously isn't an A/C circuit. The 9425 has an input impedance of 30kOhms +/- 5% and I additionally supply a 1kOhm in series for good measure. This is a 12V power supply with a common ground. The flow meter manufacturer is very poor on communication, but has more or less stated this is fine. I question their tech support.
I assume the 10V (ON state requirement) / 30kOhm input impedance = how the minimum input current is derived? (330uA)
See attached image (apologies for the quality.)
Thank you all,
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