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Current "OVERLOAD"

428 Support
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harst043
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Joined: August 30th, 2012, 9:36 am
Country: United States

Current "OVERLOAD"

Post by harst043 » August 30th, 2012, 9:40 am

My current amplifier tells me that it is "overloaded" whenever I increase the voltage of the system I am using above 10 kV. This message, however, does not correlate to a signal that has overloaded, oftentimes there is no signal at all. Can you help?

Dale C
Keithley Applications
Keithley Applications
Posts: 2845
Joined: June 10th, 2010, 6:22 am
Country: United States
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Re: Current "OVERLOAD"

Post by Dale C » August 30th, 2012, 10:08 am

Can you tell me the Model number?
The Model 428-PROG is a current amplifier. And if you are using this unit I assume that you are not applying the 10kV across the input or floating the amplifier by 10kV.
I would expect the 10kV to be across the sample. And the current amplifier to be in series with the input low at earth ground. The current amplifier voltage burden would drop mV of the signal.
Also some protection on the input of the amplifier like two fast reacting low leakage diodes that are back to back across the input. And some series resistance to limit the current.
As far as over load condition, I would connect a current source to the input say at 1uA and test the output. See if this unit is operational.

harst043
Posts: 2
Joined: August 30th, 2012, 9:36 am
Country: United States

Re: Current "OVERLOAD"

Post by harst043 » September 11th, 2012, 6:40 am

The Model is the 428-PROG. The 10kV is being applied to a sheath flow cuvette system and the current amplifier is in light with the detection PMT. The problem I am running into is that this only happens when I am in one mode of detection. How sensitive are the cables coming into the back of the unit? Can they - up interference from the instrument table?

Dale C
Keithley Applications
Keithley Applications
Posts: 2845
Joined: June 10th, 2010, 6:22 am
Country: United States
Contact:

Re: Current "OVERLOAD"

Post by Dale C » September 11th, 2012, 6:56 am

The connections on the Model 428-PROG are coax.
I would advise to use the Keithley Model 4801 low noise coax cable for this application.
It has graphite lubrication on the shield braid to reduce the triboelectric effect.
Also the outside shield would be a guard potential giving the INPUT HI and shield and guard for low level signal integrity.

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