Trying to test SSRV and potentiometer for volatage at element while underload. Multimeter reads 240v at the element, but that reading never changes when to pot is adjusted. Is this normal? Thought i'd get the volts to incease or decrease?
potentiometer question
- Thread starter jmc922
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SilverZero
Well-Known Member
I could be wrong, but I think the frequency of an SSRV is so high that you'd never see it with a multimeter.
Deleted inaccurate information.
Edit: Ajdelange has proven that a true Rms meter will work just fine.
Thanks, wasnt sure. I was trying to test because it seems like i lost ability to control voltage. Element seems to be on full blast and i cant slow down my boil. I tried switching out the pot i had an extra no change. Could my SSVR lose its ability to regulate voltage and be stuck on full throttle?
Yes, that is entirely possible. If you have a 240v fan you can wire it up and test if the fan slows. You can essentially use anything that is 240V to use as a visual indicator.
An RMS meter would read it. Anyway, if the element gives off less power (heat), then you know its working!
Kerrbrewer
I just wanna brew!
In my experience you will see a voltage drop across a resistive device such as a potentiometer. Measure across the potentiometer for a difference in potential.
Why not try a couple bigger 120V incandescent bulbs in series? A couple 100W, maybe?
It doesn't matter what the wattage of the bulbs is as long as they are the same. But where does one buy incandescent bulbs these days? Same place he buys a voltmeter that doesn't read rms I suppose. A true rms meter will certainly read the voltage. These are definitely good well beyond 60Hz and probably up to 10's of kHz. A non true meter will also show the decline in voltage but the readings will not be correct.
The object here is to sense whether the control is varying the current. A clamp-on meter is ideal for this.
Triacs, mosfets, SCR's etc tend to fail 'ON'. It's pretty plain that this is what has happened here. It is, alas, not at all uncommon.
The object here is to sense whether the control is varying the current. A clamp-on meter is ideal for this.
Triacs, mosfets, SCR's etc tend to fail 'ON'. It's pretty plain that this is what has happened here. It is, alas, not at all uncommon.
SilverZero
Well-Known Member
If I was testing I'd just install it on an element and boil some water, then go up and down and see if the boiling rate changes.
Now you got me curious. I have a Fluke 117 true Rms multimeter. And when I tried to measure the voltage on mine it didn't show anything. Does this now mean that my meter is broken? I had to use my works O-Scope.
Doesn't sound good. If the scope measures a voltage the meter should too though the scope will, presumably, have a much higher bandwidth. Try the meter on an electric outlet.
I did that, used it for work today and it read correctly. I'll try to measure my SSVR whenever I open my control box up again and see what I get.
yeah ssr failed. This is the second time. Think i had a bad connection at the element and the electricty arc'd to the metal box. Killing my SSR. Can you prevent these kinda things? Maybe with an inline fuse?
Something is funny here. Just to check things out I generated a 440 Hz tone on the computer and squared it and then squared that and squared that a couple of times. I then played that out through my audio interface and amplifier and put a Fluke 87 V true rms voltmeter on the speaker terminals. It read 1.03 Vrms. I then put a Fluke scope on the terminals and did the same. It read 1.04 Vrms. Note that as I squared the sine wave I now have pulses at 880 Hz so frequency response clearly is not a problem for this Fluke gear at 60 Hz. You must not be doing what you think you are doing.
Well I really appreciate what you did, just to verify that a true RMS meter will in fact work. I will double check everything I am doing. I'm sure now it's something I am doing incorrectly.
It gets a bit more interesting still. I learned something about these meters that I didn't know. They measure the rms of the AC component of the applied voltage, not the actual rms. It turns out that my audio interface has a gain of 1.04 with respect to the numbers passed to it and it is DC coupled (unlike the amplifier I used in the experiment last night). Thus if I generate a sinewave with peak amplitude 1.00 in the computer a signal with amplitude 1.04 V appears at the output of the interface. A sin^8 wave (a series of pulses at 880 Hz) with peak amplitude 1 has, at the output of the interface, an rms voltage of 461 mV consisting of a DC component of +284 mV and and AC component of 363 mV. The Fluke 87V read the DC as 283 mV and the AC component as 365. The Scopemeter read the rms as 458 so this Fluke stuff is pretty good gear (but we knew that, didn't we?). The important finding here is that the 'True RMS' reading in AC mode on a Fluke True RMS meter is the true rms of the AC component of the signal or, put another way, the meter is AC coupled when in the AC mode. If you want the real RMS of the signal you will have to make an AC measurement and a DC measurement and compute
Vrms = sqrt(Vac^2 + Vdc^2)
Vrms = sqrt(Vac^2 + Vdc^2)
