frequency of a controller

[Designer69]

good afternoon, I am trying to figure out how I can determine the operating or output frequency of a valve controller I am working with.

the input power is 120VAC @ 60HZ but I want to find what the operating or output frequency is. There are no wireless signals just wired analog and digital outputs.

would you try to contact the vendor and ask? maybe look at the operation manual?

let me know if you need additional info.

Thank You

 

[mcclary's electrical]

good afternoon, I am trying to figure out how I can determine the operating or output frequency of a valve controller I am working with.

the input power is 120VAC @ 60HZ but I want to find what the operating or output frequency is. There are no wireless signals just wired analog and digital outputs.

would you try to contact the vendor and ask? maybe look at the operation manual?

let me know if you need additional info.

Thank You

You need the right software to communicate with the valve. I would definately contact the man. and ask questions. I don't think you can simply measure voltage at the valve with a meter. You'll need a laptop for this one

 

[SG-1]

An oscilloscope can measure the frequency.

 

[mcclary's electrical]

An oscilloscope can measure the frequency.

on a digital output? never tried it

 

[gar]

101001-1639 EST

I do not understand the question.

Please describe the system.

Apparently there is some sort of valve that is remotely controlled. I will assume the valve is opened and closed with an electric motor. Is that correct? What kind of motor? DC, AC, constant speed or variable, stepping, or something else?

What frequency do you want to measure and why? Is there a tach or encoder on the motor? Are there limit switches? Is the motor torque limited?

If you know the frequency of whatever is to be measured, then how will this information be used?

.

 

[SG-1]

I have captured the IR signals from TV remotes with mine, which is a digital signal. I was only trying to determine if it was dead or alive at the time.

 

[mcclary's electrical]

101001-1639 EST

I do not understand the question.

Please describe the system.

Apparently there is some sort of valve that is remotely controlled. I will assume the valve is opened and closed with an electric motor. Is that correct? What kind of motor? DC, AC, constant speed or variable, stepping, or something else?

What frequency do you want to measure and why? Is there a tach or encoder on the motor? Are there limit switches? Is the motor torque limited?

If you know the frequency of whatever is to be measured, then how will this information be use
.

I think he's speaking of a proportional valve. No motor involved

 

[GeorgeB]

good afternoon, I am trying to figure out how I can determine the operating or output frequency of a valve controller I am working with.

the input power is 120VAC @ 60HZ but I want to find what the operating or output frequency is. There are no wireless signals just wired analog and digital outputs.

would you try to contact the vendor and ask? maybe look at the operation manual?

let me know if you need additional info.

Thank You

I deal with hydraulic proportional valves, and use 2 techniques; the manual and my Fluke 87 which measures frequency. If PWM is used, the meter will work. I don't understand the reasoning for it, but PPM is used more and more which doesn't give good frequency info. The oscilloscope referenced by a previous poster will give information on the signal.

 

[Designer69]

101001-1639 EST

I do not understand the question.

Please describe the system.

Apparently there is some sort of valve that is remotely controlled. I will assume the valve is opened and closed with an electric motor. Is that correct? What kind of motor? DC, AC, constant speed or variable, stepping, or something else?

What frequency do you want to measure and why? Is there a tach or encoder on the motor? Are there limit switches? Is the motor torque limited?

If you know the frequency of whatever is to be measured, then how will this information be used?

.

1. the valve is a drag valve, pneumatically controlled. there is a digital controller which takes in a 4-20ma input process signal and regulates air to the valve for positioning.

2. I want to measure or know the operating or output frequency of this digital controller. why? because it failed its EMI qualification testing for EMI emmissions at a frequency of 63 and 149.9 MHz. all other frequencies from 30 to 200 MHz passed.

3. If I know that the operating frequency of the digital controller is always... lets say 80MHz, then I can conclude that since the controller will never operate at 63 or 149.9 MHz, no filtering or shielding is required.

however i have a feeling it probably is operating at 63 and 149.9 MHz since those are the frequencies it caused the most EMI.

Thanks guys

 

[gar]

101004-1523 EST

Designer69:

Those MHz signals are very high for anything directly related to the 4-20 MA signal or pulse width modulation to the proportional valve. Thus, they likely are from clock signals in the proportioning controller.

Do you have a spare controller that you can open up and look for crystal frequencies inside the controller. Unless someone is trying hide something, the frequency of the crystal will usually be marked on the top of its can.

How precisely do you know these frequencies? I do not see a quick easy sub-harmonic. Maybe there are two crystals. How sharp are these signals? Spread over a wide range or narrow?

I suspect you may need to do filtering and shielding.

.

 

[Designer69]

I would think EMI qual test would need to drastically exceed acceptance criteria limits though. This particular test just barely exceeded it. Would you still filter and shield?

 

[gar]

101004-1607 EST

If you have a qualification test that must be passed, then you have to do something about the problem.

You need to get inside and probe for the frequency sources. Once identified, then try to figure out how to reduce the level.

First, use your eyes, then a scope with several hundred MHz bandwidth. A frequency meter is not likely to help much. An AC voltmeter with a GHz bandwith might be useful. You need to find the oscillator that is the source, and then figure out how to reduce the EMI from it, and other sources.

Why is this not the responsibility of the manufacturer of the controller?

.

 

[steve66]

I'm confused. Is the qualification test to make sure the valve controller doesn't cause interference with other equipment? Or is it to make sure the valve controller isn't susceptable to interference from other sources?

The manual on the controller or the manufacturer should be able to give you some info.

VFD's sometimes have programmable "skip" frequencies to eliminate problems with motors having vibrations at certain frequencies.

But I've never heard of a valve controller having this. To be honest, I never saw a valve controller that used PWM signals. I thought most just ran on a 4-20 ma or 0-10V DC output. Unless they use PWM to get the DC signal - but that sounds a lot more complicated than it would need to be.

 

[ELA]

Are you failing conducted or radiated emissions testing? What standard are you testing to?

Your best debug tool is a spectrum analyzer using a sniffer probe or a high frequency current probe if cable radiation is the issue.

You may be able to get a way with adding ferrite beads to cabling if that is the suspected emission path.

 

[Designer69]

you guys are good! ELA yes the controller is failing Radiated Emissions. I am using the Military standard in EPRI TR-102323.

the reason the mfg is not handling this is because they were already built and we JUST got the test report haha.

my plan is... since these passed every other test except radiated emissions and even that barely failed with the slightest of margins, I was going to write an evaluation basically saying: since there are no other digital components in the nearby area susceptible to EMI, no further shielding is required.

I hope you guys would agree with that, if not I need to work with the mfg to bring them back and bolster up that enclosure.

thanks

 

[ELA]

I do not see how they would let you off by stating that there are no nearby components that may be susceptible? Generally speaking a standard is a standard and you must meet the emission levels. Good luck but if that does not work...

Have you tried adding 2-3 turns on all cables exiting the enclosure through a ferrite bead? You said you were just barely failing and this is a common fix when that is the case.

The frequencies you listed are relatively low (in terms of radiated emissions).
If you go with the ferrite, research materials that have the greatest attenuation at the lower frequencies.

One of the most common places for radiated emissions to emanate from are the cables. That is why you see so many ferrites on products cables.

In the EMI world they have a saying, "Ferrite is your Friend "

Generally slot antennas in the enclosure are only the culprit at much higher frequencies.

It is tough to work through these types of problems without a Spectrum Analyzer, antenna, current probes etc. Otherwise you are at the mercy of the test house and that is expensive.

Best of Luck