Tektronix Technical Forums are maintained by community involvement. Feel free to post questions or respond to questions by other members. Should you require a time-sensitive answer, please contact your local Tektronix support center here.

Keithley 428 overloaded and possibly damaged

428 Support
Post Reply
pice.chen
Posts: 1
Joined: September 11th, 2014, 12:04 pm
Country: United States

Keithley 428 overloaded and possibly damaged

Post by pice.chen » September 11th, 2014, 12:11 pm

Our Keithley 428 is showing "overload" error message every 2sec. This happened after a device breakdown in the middle of a measurement.
I wander if the current amplifier is still functioning.
If so, how to suppress the error message?
If not, I assume we will need a repair service.
Thanks!

Dale C
Keithley Applications
Keithley Applications
Posts: 2842
Joined: June 10th, 2010, 6:22 am
Country: United States
Contact:

Re: Keithley 428 overloaded and possibly damaged

Post by Dale C » September 12th, 2014, 6:08 am

Overload means the input signal is larger than the gain setting.
Are you able to decrease the gain setting. For example if you are on 1e6 gain, try setting it to 1e5 gain.
What does the applied signal look like? Is it an AC signal with a 0.5Hz bandwidth?

dm1181
Posts: 1
Joined: August 10th, 2015, 9:09 am
Country: United States

Re: Keithley 428 overloaded and possibly damaged

Post by dm1181 » August 10th, 2015, 12:56 pm

I am having the same problem. The overload message is flashing, even at low gain settings, and even with no input plugged in. I believe I incorrectly configured my setup, with positive and ground leads reversed from a voltage source. Around 10-15 volts my current reading on the oscilloscope became inconsistent, and I think the unit may now be incorrectly grounded? If I connect a BNC input with a negative alligator clip to the chassis ground, the overload message disappears, but the oscilloscope displays a nonzero reading. I tried performing a zero correct but this did not change the reading. Any help would be appreciated.

Dale C
Keithley Applications
Keithley Applications
Posts: 2842
Joined: June 10th, 2010, 6:22 am
Country: United States
Contact:

Re: Keithley 428 overloaded and possibly damaged

Post by Dale C » August 11th, 2015, 6:05 am

Can you set the gain to 1e6 and input 1uA?
Then see if it displays OFLO.
If so, set the gain to 1e5 and see if that helps.
If not the unit may need service.

Post Reply

Return to “Curent Amplifiers”

Who is online

Users browsing this forum: No registered users and 1 guest