impedance problem

[JPI]

Hi I need to read the voltage from a power supply, the datasheet for the power supply states that any digital measuring device needs an input impedance of at least 10M Ohms, unfortunately the Digital measuring device I have states that the maximum input impedance is 1M Ohm. What options do I have? Is there a circuit that can increase the input impedance of my measuring device?

Regards

John

 

[Nigel Goodwin]

Yes, an opamp amplifier or buffer - but it sounds completely pointless, a 1M 'impedance' should be perfectly fine - what EXACTLY are you trying to measure?.

 

[JPI]

Hi Thanks for your reply

Here is the extract from the data sheet, it is a 1KV Glassman MK series.

Voltage monitor. J1-4
A 0-10v signal, positive with respect to common, and in direct proportion to output voltage, is available at this pin. a 10k Ohm limiting impedance protects the internal circuitry so that a digital voltmeter with greater than 10 Megohms input impedance should be used to monitor this output. It is also acceptable to use a 1 mA DC full scale instrument (i.e analog meter) for monitor purposes.

I am not using a multimeter to monitor the voltage I am using a labjack u3-HV.

I have a very tight budget so I am stuck with what I have already got.

Regards

John

 

[Nigel Goodwin]

Do a bit of ohms law

Work out the voltage drop across 10K with a 1M load (it's not a lot, and nothing to worry about).

Do you have the circuit for the labjack u3-HV?, you could decrease the input resistor (to make it 990K), and thus compensate for the 10K in the source, but I doubt it's worth it.

 

[JPI]

Thanks

I was more concerned about weather the power supply would somehow damage the labjack, but its clear now that its all about the accuracy of the measurment and as the error is so small I am no longer concerned.

I could clearly do with some electronics tuition

Thanks again

Regards

John