RTD Data Acquisition 8-Layer Stackable HAT for Raspberry Pi

Compatible with all Raspberry Pi versions from Zero to 5, the RTD Data Acquisition Card offers a compact and inexpensive solution for reading and storing data from up to 64 PT100 temperature sensors. Using 24-bit delta-sigma A/D converters with four channels each, the card achieves better than 0.1% accuracy. Field calibration with a precision 100Ω resistor can lead to 0.01% precision. Since temperature measurement using RTD is based on resistance, the resistance in the lead wires and connectors must be considered when calculating the overall resistance in the system circuit. A 3-wire circuit design allows lead wire resistance to be factored out of the overall calculation.

• Compatibility: The card is compatible with all Raspberry Pi versions from Zero to 5. It shares the I2C bus using only two Raspberry Pi’s GPIO pins to manage all eight cards. This feature leaves the remaining 24 GPIOs available for the user.
• Power Requirements: The card needs 5V to operate and can be powered from the Raspberry Pi or its plugable connector. It requires 50mA to operate.
• Stacking Multiple Cards: Up to eight RTD Data Acquisition cards can be stacked on your Raspberry Pi. The configuration DIP Switch, labeled ID0, ID1, and ID2, has three positions to select the stack level. Cards can be stacked in any order.

Board Layout

Electrical Specifications / Mechanical Specifications

Features

• NEW: V7 supports PT100 and PT1000 sensors
• NEW: Sensor selection in software. No jumpers!
• NEW: 5A current transfer for Raspberry Pi 5
• 24-bit delta-sigma A/D converters
• Factory accuracy: 0.1%
• Maximum accuracy (through calibration): 0.01%
• Maximum acquisition speed 40 cps
• Eight-layer stackable to 64 RTD channels
• RS485/MODBUS transceiver
• PT100 sensors, -200°C to 765°C range
• PT1000 sensors, -50°C to 500°C range
• Programmable threshold LEDs on all inputs
• Pluggable Connectors 26-16 AWG wires
• The onboard hardware watchdog can power cycle the Raspberry Pi
• 5V power supply provides power to the Raspberry Pi
• General Purpose Pushbutton
• Onboard resettable fuse
• RTD DAQ Raspberry Pi
• Uses only the I2C port, all GPIO pins available
• Works with any Raspberry Pi from ZERO to 5
• ECCN Code EAR99
• Command line 
• Python library
• Node-Red nodes
• Modbus RTU
• CODESYS Driver
• OpenPLC module
• Arduino Library
• Home Assistant Integration

The Revision 6.x of the RTD card has an RS485 transceiver, works with PT100 sensors, and has programmable LEDs indicating the status of all inputs.

Software

Software Interfaces: You can write your own Data Acquisition system in C, C++, PERL, or the language you choose using the Command Line functions or the Python Library. A browser interface can easily be deployed using Node-Red.

Field Calibration: An external high-precision resistor can achieve precision of field calibration to 0.01%. Software commands permit the user to calibrate the card at two points (the 2 points must be as far as possible but inside the measurement range). The resulting values are stored in flash and used for resistance measurement compensation, which will be reflected in the temperature readings. The resistance to temperature conversion is made by the most straightforward equation T = (R-R0)/(R0*k), where T is temperature in Celsius degrees; R is the sensor resistance; R0 is the resistance at 0 deg Celsius (100 for PT100, 1000 for PT100), and k 0.00385. The resistance measurements are available if the user uses the polynomial equation.

RS485/MODBUS Communication
The RTD Data Acquisition card contains a standard RS485 transceiver that the local processor or a Raspberry Pi can access. The desired configuration is set from two bypass jumpers on the configuration connector J3. See in the CARD LAYOUT jumpers “485-RX” and “485-TX”. Raspberry Pi can communicate with any device with an RS485 interface if jumpers are installed. In this configuration, the card is a passive bridge that implements only the hardware levels required by the RS485 protocol. To use this configuration, you need to tell the local processor to release control of the RS485 bus:

~$ rtd [0] rs485wr 0 0 0 0 0
If jumpers are removed, the card operates as a MODBUS slave and implements the MODBUS RTU protocol. Any MODBUS master can access all the card’s inputs and set all the outputs using standard MODBUS commands. A detailed list of commands implemented and parameter addresses can be found on GitHub. In both configurations, the local processor must be programmed to release (jumpers installed) or control (jumpers removed) the RS485 signals. For further information, see the command-line online help.

LED threshold signals: The RTD Data Acquisition card has eight LEDs that can be activated when the input reaches a preset threshold. The software can set the threshold for each input.

Firmware Update: A command can update the card firmware in the field. The update is made with the latest firmware version located on our servers. More instructions about the process can be found on GitHub. Please make sure there is no process, like Node-Red or Python scripts, that tries to access the card during the update process.

RTD Data Acquisition Downloads

• User’s Guide V6.0
• User’s Guide V6.2
• User’s Guide V6.3
• Hardware Schematic V6.0
• Hardware Schematic V6.2
• Hardware_Schematic_V7.0
• 3D-STEP MODEL V6.2
• 3D-STEP MODEL V6.3
• Command Line
• Python Library
• Node-RED Nodes
• 2D CAD Drawing
• 3D Printing Enclosure
• CODESYS Library
• RoHS and REACH Compliance Declaration

Whats Included

8-Channel RTD HAT for Raspberry Pi

Mounting hardware

• Four M2.5x18mm male-female brass standoffs
• Four M2.5x5mm brass screws
• Four M2.5 brass nuts

All female connector plugs

Quick Start

1. Plug your card on top of your Raspberry Pi and power up the system
2. Enable I2C communication on Raspberry Pi using raspi-config.
3. Install the software from github.com:

• ~$ git clone https://github.com/SequentMicrosystems/rtd-rpi.git
• ~$ cd /home/pi/rtd-rpi
• ~/rtd-rpi$ sudo make install
• ~/rtd-rpi$ rtd

The program will respond with a list of available commands.