While programming a 4200A for stress measurements, I noticed something interesting and probably dangerous: Disabling a channel has no effect on a SMU which standby mode was set!
I want to perform a stress measurement and thus keep, say, SMU1 active after the measurement. I can do so by using the following commands with the appropriate parameters (in particular, with those for SMU1)
- "DE CH" (channel definition),
- "SS VC" (output configuration),
- "ST" (disable standby, used on SMU 1)
- "MD ME" (perform measurement)
Problems start when I want to disable (physically disconnect) SMU 1 after some time. The reference manual states that this can be done with using the "DE CH" command. However, after doing so the constant voltage on SMU1 remains! Even worse, if I now configure and perform a different measurement on different SMUs, not even having SMU1 in the channel definitions anymore, the constant voltage on SMU1 STILL remains! This is dangerous both for devices and humans.
Can you reproduce this issue?
I also played around a little bit to understand what is happening and found another issue: In a subsequent test, I explicitly enabled standby on SMU1 before performing the first measurement (stated above, involving SMU1 again). As expected, SMU1 now goes into standby mode after the measurement, which means it forces 0V. BUT if I disable the channel now, the output seems to keep actively forcing 0V. This was difficult to measure using a simple volt meter. I used the capability of my voltmeter to measure resistance, the result I got was "0 Ohms", but I expected a very high resistance, or the voltmeter status "Disconnected".
Can someone from Tek reproduce this? And would someone please comment on this behavior?
How can I be sure that “DE CH” physically disconnects a SMU after having used it?
Is it actually intended that I cannot physically disconnect an output, even if I only explicitly enabled standby mode, which is the default setting anyway?
Is the standby mode affecting this behavior at all, or does it also occur when standby mode is untouched?