#22, M1S: RTD Temperature Meter
Function: RTD temperature meter
Form factor: M1S
Category: Input module
Special needs: ---
Power requirements: 5V/10mA
Mates with: #19, #20, #21
See also: #29
Tibbit #22 is based on the MAX31865 15-bit RTD-to-digital converter IC. This Tibbit can work with platinum RTD sensors (PT-RTDs) in the 100 Ohm to 1000 Ohm range. Our Tibbo BASIC demo application (see below) supports PT100, PT200, PT500, and PT1000 sensors (this is selectable in code, see the main.tbs file).
In addition to the MAX31865 IC, this Tibbit also carries a PIC16F1824 microcontroller. The microcontroller interfaces the converter IC to the main CPU of the TPP board. With the right firmware, it can also be used for data preprocessing (for example, for averaging of measurements with the purpose of increasing measurement precision).
Combine this Tibbit with #21 (four terminal blocks), #20 (nine terminal blocks) or #19 (DB9M connector). It's not common but possible to use the latter for wiring into the meter's inputs.
Tibbit #22 is very accurate. Here are the results of measurement comparisons between the Tibbit #22 and a Fluke 726 process calibrator:
- PT100 sensor: Measurements performed by the Tibbit deviated from those of the calibrator by no more than 0.5 degrees C in the temperature range from -100C to +400C. The error did not exceeded 2.5 degrees C outside of this temperature range.
- PT1000 sensor: Measurements performed by the Tibbit deviated from those of the calibrator by no more than 0.5 degrees C in the temperature range from -125C to +550C. The error did not exceeded 2.5 degrees C outside of this temperature range.
Connecting the RTD sensor
You can use 2-wire or 4-wire sensor connection. The 2-wire connection does not allow the system to compensate for errors caused by cable resistance. Therefore, this type of connection is suitable for cases where the sensor cable is short:
The 4-wire connection eliminates errors caused by cable resistance. It is recommended for cases where the sensor is located at some distance from the Tibbit.
There are two red, one yellow, and one green LED. The first red LED is connected to the SCL line of the I2C interface, the second one — to the -RST line of the PIC micro. The yellow LED is connected to the SDA line of the I2C interface. The green LED is on the -INT line.
The use of this Tibbit is illustrated by a Tibbo BASIC test project. Yo can find it here: https://github.com/tibbotech/CA-Test-Tibbit-22.