Post by Professor Lake Shore on Jan 31, 2017 17:02:20 GMT -5
I seem to be experiencing signal issues with my triax cabling and ZN50 probe blade – loss of continuity, shorting between the signal connector and guard electrode, or higher than normal noise. What may be causing this?
The micro-miniature cabling used in the cryogenic probe station is extremely delicate and mishandling of the cable when exchanging probe blades can damage the internal conductors. Damage is typically caused when the cable behind the SMA nut is not held steady when attaching or detaching the SMA connector the ZN50 probe. The friction from the turning SMA nut will apply a torque to the cable and the resulting twisting action will break or distort the cable conductors. A broken center conductor in the cable usually manifests as a loss of or intermittent continuity between the center conductor and probe blade. Similarly, a damaged guard electrode on the triax cable can short the guard to the center conductor or break the guard path. In the case of a broken guard path, higher than normal noise or current transients may be observed. To verify whether damage has occurred, the first step is to carefully measure the continuity between the feedthrough electrodes and the probe blade. Excess force applied to the probe blade can cause damage. If the resistance is not a fraction of to a few ohms, the cable must be replaced (the procedure to replace the cable is described in the reconfiguring cables section of Chapter 5 in the probe station user manual). The second step is to check isolation between the signal, guard and ground; this is most easily achieved by measuring the resistance between each electrode of the triax feedthrough. Damaged cables will often have megaohm-level resistances between one or more of the electrodes and need to be replaced.