Post by Professor Lake Shore on Jan 31, 2017 17:41:55 GMT -5
When setting excitation current in my Hall system, I want the current high enough that the desired voltage is large compared to the unwanted signals but not so high that it adversely affects my measurement and damages my sample. How can this be done?
This is a multi-step process. First, use the toolbox resistance measurement to find a current the produces a voltage across the contact between 0.1 volt and 0.01 volt. This is a range that we find useful, but you may have to move out of this range depending on the material and the contacts. We typically start at a milliamp of current and move up or down from there to find a starting voltage. For the sake of discussion, assume the current is 10 microamps. Then go to measurement section and select only ohmic check. Set the max. current to value selected in the toolbox (10 microamp in this case) and the min. current to 1/10th of the max. current (1 microamp in this case). Set the number of points 5 and run the ohmic check. If the correlation is 0.9999 or higher, you are good to go. If the correlation coefficient is less than 0.9999, try decreasing the max. current and min. current by a factor of 3 and repeat the ohmic check. The purpose of this is to eliminate self-heating, which will distort the linear ohmic check. This is particularly important if the AC field option is used. Self-heating during an AC field measurement can inject noise into the measurement. Sometimes, decreasing the current used in the AC field measurement can increase the signal to noise ratio of the measurement.