Good day folks
I work with heavy earthmoving equipment supporting the service spectrum, more frequently we meet with E.C.U.'s controlling P.W.M. proportional valves. As I understand a oscilloscope is needed to establish if the signal comping from the E.C.U. is correct, experience tells us that either the signal works or fails. My question is can a simple device establish if the signal is working or not as the case may be.
Thanks

 

Welcome to AAC.

Yes, there is more than one way to check a PWM signal. Which would make the most sense for your application will depend on what you are testing. If the valves and ECUs are always using the same signals then it is simplest. You would just need something that can “listen” to the PWM signal and check that it is within the required tolerances.

The easiest way to do this is with an MCU (MicroController Unit) like an Arduino compatible MCU module. It would be able to measure the signal and display either the frequency or a go-no go indication. It could also check the signal level if that‘s useful.

The implementation will depend on the actual devices under test.

 

Some multimeters can measure frequency and duty cycle, which is probably enough to tell you if the signal is good.

Bob

 

Some multimeters can measure frequency and duty cycle, which is probably enough to tell you if the signal is good.

Bob

There are probably several test instruments that can do the job as part of their function. I had the impression the TS wanted a go-no go sort of box that would make checking as simple as telling red from green.

For that matter, there are PWM testers for hobby servos that read out the PWM signal digitally, but whether those can be readily used in this application isn't clear.

I would say a good DMM with frequency and a simple procedure for checking the frequency (and/or duty cycle) and signal level would be the most appropriate solution if such a procedure was practical for the TS' staff.

 

There are probably several test instruments that can do the job as part of their function. I had the impression the TS wanted a go-no go sort of box that would make checking as simple as telling red from green.

For that matter, there are PWM testers for hobby servos that read out the PWM signal digitally, but whether those can be readily used in this application isn't clear.

I would say a good DMM with frequency and a simple procedure for checking the frequency (and/or duty cycle) and signal level would be the most appropriate solution if such a procedure was practical for the TS' staff.

Thank you for your response, I'm not sure of the frequency whilst it is a 5 volt circuit, and I'm fairly sure the switching is made from the ground side. The device you are suggesting I guess is components you would assemble, as to the specifications the manufacturers do not make that information public. Most of the service guys have multimeters, but few have any frequency read-outs.

 

If I understand your PWM signal correctly (switching between 0 and 5V), a straight DC test would indicate its mere presence. A simple low-pass filter fed by the signal should give a voltage proportional to the duty cycle. A simple peak detector should indicate something >4V.
There are various waveform-viewing/measuring apps for phones and PCs, which should enable the frequency and duty-cycle to be checked.

 

Thank you for your response, I'm not sure of the frequency whilst it is a 5 volt circuit, and I'm fairly sure the switching is made from the ground side. The device you are suggesting I guess is components you would assemble, as to the specifications the manufacturers do not make that information public. Most of the service guys have multimeters, but few have any frequency read-outs.

Here is something that could probably be adapted.

 

I have a low frequency 10Hz PWM signal controlling my cars fan. I have found that with a straight DC volt meter, I will read ~13.8V at 100% duty cycle, ~6.9V at 50% duty cycle etc. I'm not able to measure frequency and not sure if this will work on higher frequency signals.

 

I have a low frequency 10Hz PWM signal controlling my cars fan. I have found that with a straight DC volt meter, I will read ~13.8V at 100% duty cycle, ~6.9V at 50% duty cycle etc. I'm not able to measure frequency and not sure if this will work on higher frequency signals.

It should follow that duty cycle affects average voltage independently of the frequency.

 

If I can establish the parameters of the signal my line of thoughts follow giving the correct signal by an independent source, while I competent with high pressure hydraulics and basic electrics I am dipping my toe into electronics as you may have established.
My objective is to establish the signal parameters
Offer an independent source as a temporary solution.
I'm sure you guys are far more familiar with such device's than I as I am picking your knowledge as a learning curve.
Keep in mind my next big birthday will begin with a figure eight, so learning & following may take a little more time.

 

My objective is to establish the signal parameters

Can't you just borrow an oscilloscope for a few minures to check the waveform?

 

Unfortunately there are many instances requiring a fix worldwide the chances of having an oscilloscope is not so likely, most of the cases we are dealing with over the web.

 

Diagnosing problems remotely over the web is a whole new ball-game.

My question is can a simple device establish if the signal is working or not as the case may be.

A DMM is about as simple as it gets for detecting the presence of a PWM signal and an indication of its average voltage. The average would depend on the duty cycle of the PWM.
As for whether those are what they should be (i.e. "working"), or not, for the equipment under test would rely on you having knowledge of the expected signal parameters. If the manufacturer of the equipment can't/won't reveal those then you would have to test comparable equipment for yourself.
I understand that the PWM signal for proportional valves is often 'dithered', to overcome stiction. That adds an unknown to the equation and makes use of an oscilloscope even more desirable.

 

I work on systems like this on occasion and I purchased an old Iwatsu 20 Mhz oscilloscope
and have used it a lot. The duty cycle and voltages can vary from manufacturer to
manufacturer. Most of the equipment I have dealt with the duty cycle is 5% to 95%.
If I was working on equipment electrical a lot I would either purchase a laptop based
oscilloscope or a small handheld unit for the portability. The 20 Mhz oscilloscope is
overkill for the frequency required.