I recently purchased 2 little voltmeters they look like the sort that would go in a control or instrument panel they are connected with just 2 wires which provide the operating supply ( they light up green and red) however the green one states it will work between 20and 500 volts and the red one between 60 and 480 volts. When they are both on the green one indicates normally around 241 volts the red one shows 235 volts why the discrepancy I know it's not much but makes you wonder if one of them is lying. Secondly I've noticed that the green one tracks voltage changes faster than the red one and that a few times the green one jumps down to 238 then up to 241 multiple times while the red one stays the same and I think can see a slight flicker in my filament lamps when this is happening incidentally both meters are connected to the same plug a 2 pin 5 amp one
We are using meters to provide us with information throughout the day, you have to know when good enough is good enough when it comes to what the meter is indicating and assessing the result.
The specification for an all singing and dancing Megger MFT 1741
Open circuit voltage
5 V ±1 V
Fluke T6-600
AC voltage
±(1.5 % + 2 counts) 45 Hz - 66 Hz
How do your voltage meters compare with those testers, which I presume cost significantly more than your voltage meters?
Then you have to remember that AC voltage is all over the place, if you used a moving coil meter the needle would not stay steady it would have a bit of a wobble on it.
The digital meters are just displaying a snapshot in time and are probably giving sufficient information for most applications.
Hi I'm going to borrow a calibrated meter which is up to industry standards and compare it. It's true I have fallen into the trap of thinking because they digital and brand knew they must be right which ought to be true but isn't. I have a vacuum tube voltmeter which I will try to see how wobbly the voltage is the meter is unearthed despite being in a metal case before I connect it to full mains il try it with a bulb in series just in case there's any issues how glad am I I've got a 10mA RCD socket supplying my test bench now. Thank you all for your very informative replys x Kelly
It might be instructive to have an electronic device, say domestic dimmer circuit feeding a TH lamp at half power, on the bench while you test your meter and see if it appears more accurate when the lamp is switched off.
If it does, this would indicate that harmonics are affecting the apparent accuracy.
As you drive you speed up and slow down, there are traffic lights to stop at, slow drivers in front of you and general delays.
There are two types of speed cameras.
The fixed cameras record your peak speed at one specific point on the road, so long as you don’t pass that camera at more than the speed limit you won’t get a ticket in the post. So you can have a higher peak speed in between those cameras as it is is only a snapshot of your speed at a specific point in your journey.
The average speed cameras calculate your speed over a certain distance, again you can pull out and exceed the speed limit to pass a slow vehicle without getting a ticket in the post as your average speed was low because you were behind that slow vehicle.
My new sat nav calculates the average speed I am doing between the cameras, which allows judgement calls on the likelihood of getting one of those tickets in the post. However the authorities are aware of this and locally on the A449 above the Claines roundabout there is often a mobile traffic camera van parked in front of the fixed speed camera to catch those who are speeding then slow down to pass the camera.
Now apply the same principles to volt meters. The voltage is rising and falling at 50 hertz, fifty times a second it rises and falls, in fact it passes through zero a hundred times a second, also the load changes increasing and decreasing the peak voltages, Just like a driver driving through Nottingham constantly adjusting the speed of the vehicle, voltage rises and falls.
A volt meter can be measuring the peaks or it can be measuring the average and there can be a variation in how often it does it.
Do neither of your meters is showing the peak voltages will be showing the highest voltage present. But I’m not the guy to go into detailed explanations of what volt meters you should choose for what you need to determine.
I just work on the basis that the AC volt meters I use give an indicative value allowing me to have some sort of idea of what is going on, not an absolutely precise measurement.
Depending on what you are trying to determine you might be better buying a peak voltage adapter for your multimeter or using a meter that will display the peak voltage.
Someone with more knowledge is going to have to explain the ins and outs of peak voltage measurement.
I do know that there are higher voltages than your meters are displaying.
Can I ask what's a TH lamp? I will do some tests with my variac and see what results I get if I can get a TH lamp it wil be interesting to know if my mains has harmonics in it I have come to the overall conclusion is that because my 2 new meters and my multimeter all show figures within about 5 volts of each other I can safely say my supply is around 240 volts which is where it's supposed to be so that's good. Also the analogy with cars average and peak speeds is also helpful in that I now fully understand that digital meters don't continually read the voltage but just look at certain points in the cycle it's all making sense now. I tried my vtvm which I bought at the same radio rally as the digital meters and guess what? it don't work it lights up and the needle moves when you adjust the zeroing knob but that's all it does on both AC and DC volts so if I can't fix it il re sell it next year
