BWask (Customer) asked a question.
Trouble with F4-8MPI
We have 6 setups that use an F4-8MPI to count the teeth on a flywheel to measure engine RPM. All the setups are identical, but one periodically stops updating and holds whatever value it had when it stopped.
When this occurs, we've tried replacing the D4-450, the F4-8MPI, the base, and the sensor itself and this will occasionally fix the problem temporarily but it still happens again after a couple weeks. Only this setup seems to have the issue, the other 5 operate just fine.
Does anyone have any ideas as to why this might be happening?
You replace "D4-450, the F4-8MPI, the base, and the sensor itself". And this will "fix the problem temporarily". Did you replace all components at the same time, or one at a time. If one at a time, was the sensor the last component replaced and that temporarily fixed the problem? Could something (different than the other 5) be causing the sensor/ sensor signal to fail? Such as vibration, heat, bad/pinched cable, cable next to power wires, corroded/contaminated cable connectors, broken wire strands in connectors, weak/cracked mounting support for sensor, dirt/debris falling on gear impacting sensor, faulty/over-loaded sensor power supply, etc.
The last component that we replaced was the base, which at the time I considered plausible as the F4-8MPI apparently has a unique high speed communication channel with the D4-450 that could affect it but not impact the other modules on the base, where none had any apparent issue.
We have vibration sensors attached to each engine and they are all exposed to roughly the same level of vibration, consistently only this setup has this problem though. The cable from the sensor to the F4-8MPI has been inspected and the ends have been replaced just in case but had no results produced from it. During the last time we had this issue happen we were still getting a signal from the sensor.
The power for the F4-8MPI is coming from the 24v output on the D4-450, when measured it has still been sending the appropriate voltage and current to each module using it and the total usage comes under the 400mA budget.
I agree that it looks like the problem was with the PLC hardware (PLC, base, high-speed module) since you were getting the pulse signal to the module (and everything else looked good). It may be time to consider upgrading the PLC, as the F4-8MPI has been "retired". The D4-450 has also been "retired" but available as the D4-454 (at a rather high price). I can suggest looking into the BRX Do-more PLC. The BRX also offers high-speed modules, and the programming is a lot more fun. For example, the MATH instruction eliminates so many lines of math code, analog IO automatically converts to WX's and WY's, PLC code can be organized into user-defined program segments, data-type-defined memory, etc.