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248 not outputting low voltage

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devito
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Joined: May 9th, 2014, 4:25 pm
Country: United States

248 not outputting low voltage

Post by devito » May 9th, 2014, 4:35 pm

I am trying to use the Keithley 248 to sweep voltage from 0-1800 V in a semi-logarithmic way. Currently, I'm using the face panel to manually set the voltage and am measuring the output. The supply tracks well above 50V, but I cannot get the supply to output voltages lower than ~44. From 50 V, I can slowly step down to 7V, but cannot go any lower than that. Any ideas as to why that is? I can't find anything in the manual about issues going low. Would it be any different if I use a DC power supply (0-10V) to set the voltage or if I program it using the GPIB?

Thanks

Andrea C
Keithley Applications
Keithley Applications
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Joined: October 15th, 2010, 10:35 am
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Re: 248 not outputting low voltage

Post by Andrea C » May 9th, 2014, 5:26 pm

Are either of the filters enabled?
From the specifications/data sheet, the voltage set accuracy has a 5volt adder when the filters are in use.
Voltage Set Accuracy = 0.01% of setting + 2.5v + 5v if filter in use

Also note that the voltage regulation specs apply for values of 25 volts and higher (full load) or 50 volts and higher if no load.

devito
Posts: 2
Joined: May 9th, 2014, 4:25 pm
Country: United States

Re: 248 not outputting low voltage

Post by devito » May 13th, 2014, 10:09 am

Thanks for your response Andrea!

I had not enabled the filters, but I was not aware of the regulation specs for no load vs load. I'm planning on getting a tee divider so that I can put a load on and still drive what I need. But I still want this supply to be able to give me voltages under 25V, but it looks like I'll need to create a voltage divider network in order to get below 25V.

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