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 9425. 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?
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.)
Thanks,
R