# Can a voltmeter read micro-volts?

1. Aug 18, 2016

### Mohamed_Wael

I am a mechanical engineer who is doing an experiment to measure a pressure drop across a microchannel, the sensor is measuring around 30 microvolt/mmHg which is very low value. I would like to know if the voltmeter can read this small value or not and if not what are the alternatives so I can detect such small pressure drops.

2. Aug 19, 2016

### cnh1995

Analog voltmeters can't read this small value. I don't know about digital voltmeters, but I don't think they can either. You need to add an amplifier to your circuit to amplify the voltages to a measurable scale.

3. Aug 19, 2016

### billy_joule

Yes, microvolts can be measured. But you should select your sensor so you don't need to.
Maybe your sensor needs an amplifier, maybe your sensors range is 200bar (so ~5 Volts at FSD), maybe it's broken, find the data sheet to find out.

There are 20,0000 presure sensors sold by Mouser alone, so they come in many many flavours and many are cheap as chips, it's not worth wasting your time with the wrong sensor.

4. Aug 19, 2016

### Mohamed_Wael

thanks for your answer, actually we need to measure this low voltage because we have very small pressure drop just 10 mmHg ! can you suggest an amplifier because my background is mechanical and not electrical.
thanks

Last edited by a moderator: Aug 19, 2016
5. Aug 19, 2016

### billy_joule

No I can't, we don't even know if it needs one. Maybe it needs 30 volts supply? Maybe it needs 1 Volt? Maybe the output is digital? Or frequency? Or current? Maybe the reading is so low because it's made to measure high pressures? (In which case you'll never get any accuracy at your required range).

Like I said, find the data sheet to find out.

If you can't identify the sensor and find it's data sheet then forget it, if you don't know it's range, accuracy, min pressure reading, max pressure reading, supply voltage, max over pressure rating, output type, temperature correction, media compatibility etc etc you're wasting your time. You'll either break it or get rubbish results.

6. Aug 19, 2016

### f95toli

You can get voltmeters that can measure down to about 100nV without an external amplifier. However, they do cost quite a lot (we mainly use Keithley sourcemeters, really good but quite expensive).
If you want a "benchtop" preamplifier for this application you could e.g. buy a Stanford Research SR560; this will amplify the signal enough for you to be able to just use a normal benchtop multimeter to do the actual measurement.

Measuring signals at the level of microvolts is not very difficult if you have the right equipment.

Last edited by a moderator: Aug 19, 2016
7. Aug 19, 2016

### dlgoff

8. Aug 19, 2016

### sophiecentaur

Ahhh. That statement early places you in the younger generation. Many decades ago, we had Valve Voltmeters (VVMs) which could be made as sensitive as you liked. They had extremely high input impedance and, as long as you were prepared to calibrate them every day and use a low pass filtering to iron out the low frequency noise they worked. The display, of course, was Analogue.

9. Aug 19, 2016

### billy_joule

But is it a reasonable to suggest spending ~$2500USD on a preamp just to use this sensor? The OP clearly has no idea what sensor he has, maybe it requires 30VDC and he's providing 1VDC, maybe it'll output 5V at 200 bar, maybe his testing at 10mm Hg has already burst the diaphragm, who knows. You can buy a temperature compensated, calibrated, sensor accurate to 2% for about$20, it'll output a nice, easy to measure 0 to 5V signal (or whatever other signal you'd like) in whatever pressure range you'd like. Spend \$100 and you can get 0.2% accuracy. Trying to use the current sensor without a datasheet is a waste of time and money.

10. Aug 20, 2016

### jim hardy

Temperature gradient along a wire creates tens of microvolts of DC as does different metals at connections.

Hopefully OP's sensor can be excited with AC which will be a lot easier to amplify with a modern precision opamp.

If he'd post the link to his sensor it would make things easier.

A question well stated is half answered.

His question boils down to "How do i measure 300 microvolts?" .
The wiseguy answer would be "With a microvoltmeter."
http://www.omega.com/pptst/DP3520-PA.html

that's 5 inches of water
your washing machine can measure that.
Here's a "how it's done" type article for signal conditioning.
http://cache.freescale.com/files/sensors/doc/app_note/AN1668.pdf