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wiring for current measurement with 7700

DMM7510 7½-Digit Graphical Sampling Multimeter
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Mi Zhou
Posts: 2
Joined: April 5th, 2016, 9:20 pm
Country: Singapore

wiring for current measurement with 7700

Post by Mi Zhou » April 8th, 2016, 3:03 am

We have a DMM 2701 E coupled with switch module 7700 in the lab, and they have been around for quite a while. Now we really want to start using them for current measurement. It has no problem with DCV measurement, but it can't do DCI. I short circuit the system by using the same wiring for channel 21 or 22 (compare to the other 20 channels), which are designated for current measurement.
This might be a pretty silly question, but it has been bothering me for one week. I have never used DMM before, and the connections for potentiostat are very easy. I know that I should not connect the amperemeter in parallel, but that is the connection for potentiostat or the other channels. If I can get some help on the correct connection of 7700 for current measurement, I would be very grateful!

Thanks,
Mi

Dale C
Keithley Applications
Keithley Applications
Posts: 2842
Joined: June 10th, 2010, 6:22 am
Country: United States
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Re: wiring for current measurement with 7700

Post by Dale C » April 8th, 2016, 5:51 am

Current is measured in series,.
Take a look at channels 21 and 22.
They are normally shorted(HI to LO). This keeps the current flowing.
When you want to read the current close(energize) one of the channels. Now the current flows into the shunt in the DMM to make the current measurement.
In the circuit you want to measure current, you must "break" the current path and insert the Channel 21 HI to one side of the path and channel 21 LO to the other side of the path. Basically you insert channel 21 into the current path.
That should do it.
Another method is to use channels 1 through 20 but use a shunt resistor.
Break the current path as before and connect the channel HI and LO to the break. But place a shunt resistor across the HI and LO.
Example if you expect 1mA current then use a 1k ohm resistor. Then measure voltage.
You know the resistance, you measure the voltage you can calculate the current.
Also you could use the MX +B Math function to calculate the current for you.
Example... Set M to 0.001 and B to 0.0
Now the 1mA flows through the 1k resistor and drops 1V. The MATH kicks in and multiplies the 1V by 0.001 and you get 1mA.
Each channel has its own math function.

Mi Zhou
Posts: 2
Joined: April 5th, 2016, 9:20 pm
Country: Singapore

Re: wiring for current measurement with 7700

Post by Mi Zhou » April 11th, 2016, 2:16 am

Thanks Dale. You confirmed what I was thinking before, and now the the DMM is working well - I connect it in series. My question was very silly, but thank you! :D

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