This diagram shows how to connect the RTD to a Wheatstone bridge, and
then to a PhidgetBridge 4-Input.
A Wheatstone bridge is the classic method of measuring unknown resistances, and requires three resistors of known
values. It uses the current in each leg of the bridge to create a voltage differential between both voltage dividers. Using
the voltage differential and the three known resistors, the resistance of the fourth resistor can be determined.
To determine the resistance of the RTD, the following formula can be used:
Where
is the Bridge Value given by the PhidgetBridge (in mV/V) , and
,
and
are the resistances of the
known resistors.
Using a Voltage Divider
The alternate method requires only two resistors. This reduces the amount of error that can be introduced into the
system due to resistor tolerances. A voltage is applied to the two resistors and the RTD in series. The voltage drop
across the RTD is measured. Using the voltage drop and the values of the two resistors, the resistance of the RTD can
be determined.
This diagram illustrates how to connect the RTD to the PhidgetBridge with
R
RTD
=
R
3
× [R
2
+ V
B
× (R
1
+ R
2
)]
R
1
− (R
1
+ R
2
) × V
B
V
B
R
1
R
2
R
3