Impedance Matching Adapter

[Grey]

Hi All,

 

 

I have an observation of voltage measurement between Oscilloscope and Digital Multimeter.

The voltage is shown properly as expected at Oscilloscope but the digital multimeter shown higher.(10 times more)

Normally before connecting the DUT Signal to DAQ i will verify at Oscilloscope and DMM.

I got the difference between DMM reading and scope reading. 

is this because if Input impedance  of these devices?

From the manuals i see there is no difference in Input impedances.

 

Is it neceesary to use "Input impedance adapter" before feeding the signal to DAQ? 

 

I am using 100:1 probe for voltage measurement. (Voltage range if 350 V) 

 

is Input Impedance depends on the cable we use? 

 

because in oscilloscope we can select probe nature like 10:1, 100:1 ,1:1 etc ... but in DMM it is not possible.

 

 

 

 

 

 

[Tim_S]

This is likely not due to input impedance. Have you verified the oscilloscope is configured for a x100 probe? Is the probe switch-selectable for different ranges? Does the DMM or oscilloscope read what you expect?

[Grey]

Hi Tim,

 

I'm sure that is 100:1 PROBE Setting is selected at oscilloscope. 

Oscilloscope is reading right as expected but DMM not,

It is very strange for me.

[Tim_S]

I'd double-check the DMM was reading correctly using something like a battery. What type of signal are you trying to measure?

[Neville D]

Are you measuring a constant voltage?

[Grey]

No, i'm not measuring the constatnt voltage.

the nature of the signal is DC Pulses approx 4 pulses in a second.

though the scope is showing the waveform as expected i want to cross verify the peak voltage through DMM.

The DMM i have is Agilent 34401A.

 

i did an experiment like below :- 

 

taken two different manufacturers of 100:1 probes.

 

Probe 1  (100:1) (Manufacturer unknown)

 

connected to oscilloscope : result as expected. 

connected to DMM : Peak voltage detected to approx 30 V DC

 

Probe 2  (100:1) (PMK PHV 1000) 

 

 

connected to oscilloscope : result as expected. 

connected to DMM : Peak voltage detected to approx 6.1 V DC

 

 

 

I Intended to use PCIE6320 as my DAQ. 

Before connecting the signal to DAQ i want to verify the signal is in accpeted range.

 

thanks. 

[Tim_S]

The DMM is reading what I would expect. A DMM will report a time-averaged signal, hence your pulsing DC will go through a strait average (DC measurement) or RMS average (AC measurement). This is a matter of using the proper tool for the job.

[Grey]

Hi Tim,

Thanks for your valuable input!