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Old August 15th, 2019, 12:25 AM   #16

kallileo is offline
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You could also try to install a separate power supply/transformer just to drive valves coilsso as to isolate it from the power supply of your PLC.
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Old August 15th, 2019, 03:47 AM   #17
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These sensors are usually hall effect and are sensitive to spikes or over voltage, one other possibility is to use a separate supply common the 0v of both & fit diodes to supress the solenoids or use separate supply for solenoids.
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Old August 15th, 2019, 11:49 AM   #18
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You might also consider putting a varistor across that paddle wheel sensor.
(And the valve coils, PLC outputs etc.)

Select the Right Varistors for Overvoltage Circuit Protection

Varistors, also called metal-oxide varistors (MOVs), are used to protect sensitive circuits from a variety of overvoltage conditions. Essentially, these voltage-dependent, nonlinear devices have electrical characteristics similar to back-to- back Zener diodes.

Download this article in .PDF format

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Old August 22nd, 2019, 12:07 PM   #19
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Bunt23 is offline
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Hey I wanted to thank everyone for their input on this particular topic. I ended up buying the surge suppressor (Automation Direct calls it a "transorb module") that Keithkyll suggested. I installed it yesterday, and it worked! So thank you thank you thank you. I had a follow-up question that I would appreciate some input on now. I certainly learned the hard way about surge protection from inductive loads... but moving forward, how would I spec out the appropriate sized diode for this type of situation in the future? What specs do I need to gather from the inductive devices and what specs do I need to look at in the diodes to ensure I'm designing a good system?
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Old August 22nd, 2019, 06:04 PM   #20

Copyleft is offline
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Location: Kusatsu
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I think surge suppressor or surge killer is just a varistor, maybe inside enclosure with screen terminal.
Here in Japan SMC and CKD offer for their solenoids the option to have the varistor match your solenoid spec.
About diode question for this specific case is better varistor and one dude already posted one link to how calculate the proper size.

Diode have many videos at youtube about electronic explain that.

Last edited by Copyleft; August 22nd, 2019 at 06:10 PM. Reason: Forgot
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Old August 22nd, 2019, 06:26 PM   #21
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I went through this process a little earlier in the year, see this thread.

Most solenoids these days (in Australia at least) have surge suppression built in, so it's usually not an issue here. It's just because I was working in a non-standard application that the ones I had to use did not have it. I solved the problem by switching out the standard supply solenoid plugs for plugs with surge suppression built in. The thread I linked also gave several other options as well as some general information on diode selection if you want to do it the hard way
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