a voltage divider cirtuit.
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.
Getting Higher Accuracy
In order to get the highest accuracy from the RTD, consider the following:
Use resistors with a high degree of tolerance. There will be less variability in the manufacturing of 0.1% resistors
when compared to 1% resistors.
Measure the known resistors with an ohmmeter. By obtaining the most accurate measurements for the known
resistances, the formula will result in a more accurate measurement of the RTD.
Use a moving average when obtaining the Bridge Value to reduce the amount of noise in the measured signal.
Estimate or Measure the resistance of the +5V and GND wires between the RTD and the 1046 PhidgetBridge.
Add this resistance to the two resistors.
Turn off the power to the RTD (by disabling the channel on the PhidgetBridge) to reduce self-heating of the
RTD.
By using higher resistor values (> 1 Kilo ohm), there will be less self-heating of the RTD, but the resolution of the
measurement will be reduced somewhat. We recommend 1 Kilo Ohm resistors as a reasonable trade off.
What to do Next
Software Overview - Find your preferred programming language here to learn how to write your own code with
Phidgets!
General Phidget Programming - Read this general guide to the various aspects of programming with Phidgets.
Learn how to log data into a spreadsheet, use Phidgets over the network, and much more.
Phidget22 API - The API is a universal library of all functions and de nitions for programming with Phidgets.
Just select your language and device and it'll give you a complete list of all properties, methods, events, and
enumerations that are at your disposal.
R
RTD
= (R
1
+ R
2
) × V
B
1 − V
B
V
B
R
1
R
2
