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2182A Nanovoltmeter Channel2 Lo wire problem and reading dat

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sausgh
Posts: 4
Joined: February 8th, 2015, 5:33 am
Country: India

2182A Nanovoltmeter Channel2 Lo wire problem and reading dat

Post by sausgh » May 15th, 2015, 8:04 am

Dear All,
I am research scholar working with Keithley Nanovoltmeter 2182A nanovoltmeter. I have faced following problem and try to know the exact fault in the system. I need a technical help from technical expertise. If you know the email Id or contact detail then you can help me. Since I am not getting any reply from Indian Service center of Keithley. If you know how to fix the problem then please let me know.

I use to measure two voltages (in microvolt range) from two channel of Keithley using Labview program. Each voltage measured at the 200 micro second interval. Suddenly I observe the "overflow V" error in second channel mode. where as first channel is measuring voltages from 1 micro Volt to 10 Volt range and when measuring the known voltage by second channel in auto mode it only measure up to 1 Volt. while measuring the signal below 1 volt by second channel is not possible it takes any random value and showing overflow V at frequent interval.

troubleshooting:

I joined all the four wire and short it then it shows few micro volt signal then i press the REL button. after that i again measure but same over flow problem by second channel. so I try to sense the temperature using K type thermocouple. It shows fine data with channel one, but overflow error for second channel.

Then I use the ground wire i.e. Lo wire of first channel and connected with the Lo wire of first channel, then in this condition channel 2 is working fine and sense the voltage signal up to 1 micro voltage and sense the accurate temperature by thermocouple. So I conclude that channel 2 is working but Lo wire of channel 2 doesnt response when we are going to sens the voltage below 1 volt and show the overflow error. I try to sense the voltages from both channel by keeping both channel LO wire short at a point then both channel work fine and read the data up to microvolt range.

So how to solve the problem of LO wire of second channel. Second channel do not work until it get shorted with LO of first channel. Is this the issue of ground problem for channel 2 below the 1 volt signal. Any one can help me to fix this issue. Should I do my research to sense the voltage by both channel while keeping LO of both channel shortage. or it may damage my instrument more.

My instrument is under warranty condition. But no reply from the official Indian service centre. what should I do. Please help me and tell me how to solve the issue. I want to communicate with the Keithley head office and their technical expertise to know the solution and what makes it damage the second channel Lo wire.
I will be looking for a suitable solution.

Thanks & Regards
Saurabh Singh
Indian Institute of Technology Mandi.

Joseph V
Keithley Applications
Keithley Applications
Posts: 107
Joined: July 1st, 2014, 10:31 am
Country: United States

Re: 2182A Nanovoltmeter Channel2 Lo wire problem and reading

Post by Joseph V » May 15th, 2015, 8:22 am

Hello Saurabh,

When using channel 2 the LO should always be connected to the LO of channel 1 for low voltage measurement. Otherwise you will not get accurate measurements.
This is all detailed in section 2 of the 2182A's user manual.
Specifically under the 'pumpout current' section

-Joe

sausgh
Posts: 4
Joined: February 8th, 2015, 5:33 am
Country: India

Re: 2182A Nanovoltmeter Channel2 Lo wire problem and reading

Post by sausgh » May 15th, 2015, 8:49 am

Dear Joseph,
initially it was not the problem. Both channel were doing independent measurement of voltage and temperature, now they are not doing independent. that means if i connect independently both channel with two different thermocouple then first channel will show the data but second channel will show overflow. If this is essential to short the LO of both channel then what is the benefit to do the measurement at two different point by two channel. I thought it may be damage of second channel LO wire from inside, but still lets see it.

sausgh
Posts: 4
Joined: February 8th, 2015, 5:33 am
Country: India

Re: 2182A Nanovoltmeter Channel2 Lo wire problem and reading

Post by sausgh » May 15th, 2015, 9:07 am

Thank you Joseph,
I try to do the way you said. its fine now. Actually I was missing to make the contact between the two point which is connected to the thermocouples. Now when the two copper block in touch then I saw both the channel is reading the voltage as well temperature accurately. Thanks a lot for your quick reply.

Regards
Saurabh Singh
Joseph V wrote:Hello Saurabh,

When using channel 2 the LO should always be connected to the LO of channel 1 for low voltage measurement. Otherwise you will not get accurate measurements.
This is all detailed in section 2 of the 2182A's user manual.
Specifically under the 'pumpout current' section

-Joe

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