Hi friends!
I thought I would share a
bug report on
Keithley 2450 SMU to inform others and check if anyone here has encountered this issue.
Setup: Keithley 2450 sources 1.1mA through a ~100 ohm resistor. Keysight 34465A measures the voltage across the resistor in digitize mode (50kHz) and the results are graphed.
Result: See plot attached.
Bug: When sourcing fixed current an artifact is introduced. The plot of voltage across the resistor shows periodic spikes. At first I thought this was electromagnetic interference coming from somewhere in my lab, but the frequency is relatively low and the artifact precise and repetitive. Furthermore turning the SMU output OFF the artifact would continue, but if I turn the SMU off itself then the artifact disappears. Also if I disconnect the leads from the SMU the artifact disappears.
Artifact:
- Alternating high then low voltage/current at 0.5ms intervals.
- A burst of glitches lasts 16ms.
- 3.5ms delay between each burst of glitches.
- A series of three bursts of glitches repeats precisely every 500ms.
It looks like a 1kHz clock signal is coupled into the current source. Perhaps something in the front panel or elsewhere that is clocking 16-bits in 3 bursts, and then repeated every 500ms.
In a follow up test I connected a Keithley DMM7510 in series with the SMU and resistor while the 34465A is measuring the voltage across the resistor. I attached photos of each instrument. (In this case the SMU is sourcing 0.95mA, and I've connected the DMM7510 terminals such that its measuring negative current). See photos attached. I've also found that manually setting the "range" and changing the source current setting has an impact on the severity of the problem.
I'm on the latest firmware (v1.7.3) now but originally discovered the problem on an earlier firmware. I decided to update to the latest hoping it was fixed but it is not.
So far I contacted Keithley and they've been able to reproduce the problem.
Has anyone else experienced this?
Sparky