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Sampling rate for 2182 at 1 PLC

2182 Series Support
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Sanderson
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Joined: August 10th, 2012, 1:45 pm
Country: United States

Sampling rate for 2182 at 1 PLC

Post by Sanderson » August 10th, 2012, 4:45 pm

I am using the 2182A to measure voltage samples to calculate the integral voltage of a signal. I have the 2182 setup with NLPC = 1 and digital and analog filtering and autozeroing off. I am using a calibration source that gives a sharp square 0.01 volt 0.1 sec pulse. At 1 PLC there should be about 6 samples that "see" the pulse, but the 2182 only 4 samples "see" the pulse. Is the 2182 truly sampling at 1 PLC or is at some other sampling rate and if it is some other rate what is it? Is there anything else I can do to increase the sampling rate to be 1 PLC?

Dale C
Keithley Applications
Keithley Applications
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Joined: June 10th, 2010, 6:22 am
Country: United States
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Re: Sampling rate for 2182 at 1 PLC

Post by Dale C » August 13th, 2012, 6:02 am

The A/C converter in the Model 2182A is an integrating A/D converter.
The converter has four phases of the A/D cycle.
Signal integration is only one part of the the cycle.
Signal integration is the portion of the cycle where the A/D "looks" at the input signal and integrates it.
Then there are three other phases.
Zero Integrate
Reference Integrate
Calculate
If Auto Zero is disabled then the A/D cycle is
Signal Integrate
Calculate
In this case the timing would be more true to the PLC timing/setting, not exact but closer.
This is because the zero integrate and reference integrate would not be performed with the A/D cycle.
Take a look at the Operating Characteristics in the Model 2182A specifications.
Look at notes 13, 14, 18, 19 and 20.
These tell you the configuration to get certain speeds.
Here is the link to specs.
http://www.keithley.com/support/data?asset=15912

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