# LoZ mode on DVM meters used for?

Discussion in 'General Electronics Chat' started by willwatts, Nov 20, 2014.

1. ### willwatts Thread Starter New Member

Nov 20, 2014
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What is the low input impedance mode on DVM meters used for?

LoZ DVM input is ment for measuring circuits with high resistance/impedance circuits?
HiZ DVM input is ment for measuring circuits with low resistance/impedance circuits?

Can I make my HiZ DVM into a LoZ input by placing a 10K resistance across the Red & black terminals on my DVM meter?

2. ### Denesius Member

Feb 5, 2014
89
14
I'm not sure I'm getting this correctly (since it's not clear what property you're measuring with the DVM), but it seems to me that the only function on a DVM that would need low impedance would be the current measurement setting

3. ### alfacliff Well-Known Member

Dec 13, 2013
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428
I have a meter from wavetek with two modes, the loZ presents a lower resistance than the hiZ, working with ac circuits, leakage current from adjacent conductors can show up as errors on hiZ meters. the lower input resistance usually does away with this. your meter may be different, thats just how mine works.

4. ### MikeML AAC Fanatic!

Oct 2, 2009
5,451
1,066
It should be described in the owner's manual for the meter...

I'm guessing that alfacliff has it right. On Volts scale, HiZ mode input impedance likely 10megΩ or 20megΩ. In lowZ mode, likely 20kΩ/V to make it like an old Simpson 260...

5. ### Denesius Member

Feb 5, 2014
89
14
Besides loading down the circuit under test and introducing errors in the result, can you explain what the advantage would be?

6. ### willwatts Thread Starter New Member

Nov 20, 2014
6
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Besides loading down the circuit under test and introducing errors in the result

Yes explain

Yes the LoZ input on meters is 10K like a simpson 260
You can put a 10K resistor in parallel of a DVM meter to load the input of the DVM to be 10K and not 1Meg

When would you use a low impedance meter for what kinds of circuits or tests?

7. ### profbuxton Member

Feb 21, 2014
233
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A low impedance (10 to 20K) across meter terminals is used when measuring volts to earth on a floating supply. if HZ is used( 10-20M) on these supplies (AC) capacitive coupling can give false readings.
This method is used to find out if any leg of the supply has an earth fault, if later the other leg gets an earth fault then there is the possibility of a short circuit.
Floating supplies are widely used on railway signalling circuits so that an earth on one leg does not cause loss of supply. Also used are electronic EARTH LEAKAGE DETECTORS which raise an alarm if an earth fault is detected.
The voltage on each leg is measured with respect to "ground" and should be equal, if one leg is low or zero to ground then it has an earth somewhere.