3.5.4 Sensor Polarity
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3.5.4 Sensor Polarity
Lake Shore sensors are shipped 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.
4-lead resistors can be more dependent on lead arrangement. Follow any specified
lead assignment for 4-lead resistors. Mixing leads could give a reading that appears
correct but is not the most accurate.
DT-670-SD Diode sensor leads
Cathode
Anode
3.5.5 Four-Lead Sensor
Measurement
All sensors, including both 2-lead and 4-lead can be measured with a 4-lead tech-
nique. The purpose of a 4-lead measurement is to eliminate the effect of lead resis-
tance 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 are run separately up to the
sensor. With separate leads there is little current in the voltage leads, so their resis-
tance does not enter into the measurement. Resistance in the current leads will not
change the measurement 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.
4-lead measurement
+
+
–
–
I
V
V
I
+
+
–
–
I
V
V
I
Diode
(option only)
Resistive sensor
FIGURE 3-4
FIGURE 3-5
