Sensor Polarity; 4-Lead Sensor Measurement - Lakeshore 211 User Manual

2.6.5

Sensor Polarity

Lake Shore sensors ship with instructions that indicate which sensor leads
are which. It is important to follow these instructions for plus and minus
leads (polarity) as well as voltage and current when applicable. Diode
sensors do not operate in the wrong polarity. They look like an open circuit
to the instrument. 2-lead resistors can operate with any lead arrangement
and the sensor instructions may not specify polarity. 4-lead resistors may
depend more on lead arrangement. Follow any specified lead assignment for
four lead resistors. Mixing leads could give a reading that appears correct,
but is not the most accurate.
2.6.6

4-Lead Sensor Measurement

All sensors, including both 2-lead and 4-lead can be measured with a 4-lead
technique. 4-lead measurement eliminates the effect of lead resistance on
the measurement. If it is not taken out, lead resistance is a direct error when
measuring a sensor.
In a 4-lead measurement, current leads and voltage leads run separately to
the sensor. With separate leads, there is little current in the voltage leads so
their resistance does not enter into the measurement. Resistance in the
current leads will not change the current as long as the voltage compliance
of the current source is not reached. When 2-lead sensors are used in 4-lead
measurements, the short leads on the sensor have an insignificant resistance.
2-6
Lake Shore Model 211 User's Manual
Installation