Promax Temperature Transmitter -50 to 200 degree PT100 RTD to 4-20mA

Specifications:

• Signal input: 2-wire RTD, 3-wire RTD
• Output: 2-wire 4-20mA current, current limit: min.3.8mA, max 20.3mA
• Power supply: 24VDC
• Measuring Accuracy: 0.5% TC input, 0.2% RTD input.
• Temperature Drift: ≤25ppm/℃ F.S.
• Protection circuit: Reverse polarity connection protection
• Operating temperature: -30-+80℃
• Storage temperature: -40-+120℃
• Material: PA66
• Installation: M4x2 screw, standard head-mounted

Features:

• Two-wire 4-20 mA loop power output.
• RTD PT100 signal input.
• Linear conversion and transmission.
• 0.5% (TC input), 0.2% F.S. (RTD input) high accuracy, low-temperature drift, and long life span.
• International standard head-mounted installation.

Applications

• Industrial Automation: Interfacing precision temperature data directly into standard 24V PLC analog inputs (Siemens, Allen Bradley, Delta).
• HVAC & Chiller Systems: Monitoring extremely low temperatures (-50°C) in commercial cooling lines over 100-meter+ cable runs without signal loss.
• Food & Beverage Processing: Tracking oven and pasteurization temperatures up to 200°C.
• Remote Weather Logging: Building ultra-reliable environmental monitoring stations where voltage drops over long wires would ruin standard sensor data.

Unlock New Capabilities

• Past Projects: If you've mastered basic temperature logging using DHT22s or LM35s sitting on a breadboard, you know they fail the moment you extend the wires past 2 meters.
• The Feature Upgrade: This Promax transmitter unlocks Industrial Current Loop Topology. By converting the signal to 4-20mA, you can run wires hundreds of meters through noisy environments right next to heavy AC motors without any data corruption.
• Effort Level & Requirements: Intermediate to Advanced. You will need a 24V DC Power Supply, a PT100 Probe, and a microcontroller with an ADC (plus a current-to-voltage conversion resistor) OR an industrial PLC.
  Virtual Technician & Wiring Guide
• ⚠️ CRITICAL WARNING: This is a 24V loop-powered device. Probots Logic-Safe protocol mandates that you NEVER connect the output of this transmitter directly to the 3.3V or 5V GPIO pins of an Arduino, ESP32, or Raspberry Pi without a proper current-to-voltage converter module, or you will instantly destroy your microcontroller.

Standard Wiring (Loop Powered):

• Terminal 1 (24V+): Connect to +24V DC Power Supply.
• Terminal 2 (4-20mA Out): Connect to PLC Analog Input (+).
• The PLC Analog Input (-) connects back to the Power Supply Ground to complete the loop).
• Sensor Terminals: Connect your 2-wire or 3-wire PT100 RTD probe to the designated input screws (refer to module casing for exact pinout diagram).

Package Includes:

• 1 x Promax Temperature Transmitter -50 - 200 degree PT100 RTD to 4-20mA 

Frequently Asked Questions (FAQ)

• What temperature range is this transmitter calibrated for?
  It is factory calibrated to measure from -50°C (4mA output) up to 200°C (20mA output).
• Can I use a PT1000 sensor with this transmitter?
  No, this module is specifically tuned for PT100 RTDs (100 ohms at 0°C). A PT1000 will provide entirely incorrect readings.
• Does it support 3-wire PT100 sensors?
  Yes, it supports both 2-wire and 3-wire PT100 configurations. 3-wire is recommended for better lead-resistance compensation.
• How do I wire a 2-wire PT100 to this 3-wire input?
  Connect the two sensor wires to the main input terminals, and use a small jumper wire to short the third compensation terminal to the adjacent sensor terminal.
• What is the required power supply voltage?
  It requires a standard industrial 24V DC power supply to drive the current loop.
• Can I power this from my Arduino's 5V pin?
  No. 5V is insufficient to drive a 4-20mA current loop. You must use an external 24V supply.
• How do I read this with an Arduino or ESP32?
  You cannot connect it directly. You must route the 4-20mA signal through a 250-ohm shunt resistor to convert the current into a 1V-5V voltage drop, which your ADC can safely read.
• What happens if the temperature goes above 200°C?
  The output will max out slightly above 20mA (typically ~21mA) and will not accurately reflect temperatures beyond its calibrated 200°C limit.
• What happens if the PT100 probe breaks or disconnects?
  Most industrial transmitters will drive the current loop extremely high (upscale, ~21-22mA) or low (downscale, <3.5mA) to indicate a sensor fault to the PLC.
• How far can I run the cables from the transmitter to my PLC?
  With a 24V supply and standard 18AWG twisted pair wire, you can easily run 4-20mA signals over 1,000 meters (3,000 feet) without signal loss.
• Does the cable length between the PT100 and the transmitter matter?
  Yes. You should keep the PT100 probe as close to the transmitter module as possible (under 1-2 meters). Let the 4-20mA side handle the long distances.
• Why is my PLC reading fluctuating rapidly?
  Ensure your 24V power supply shares a common ground with your reading equipment, check for loose connections, and ensure you are using shielded twisted pair cable for the loop.
• Do I need to calibrate this module out of the box?
  No, it comes factory-calibrated for the -50°C to 200°C range. However, fine-tuning potentiometers (Zero and Span) are usually present under the casing for periodic industrial recalibration.
• Is this module waterproof?
  No, the bare PCB/module is not waterproof. It is designed to be housed inside a waterproof sensor head (thermocouple head) or an IP65+ DIN rail enclosure.
• Can I connect multiple displays or PLCs to this single transmitter?
  Yes, you can wire devices in series within the current loop, provided the total resistance of all devices does not exceed the loop's driving capacity (typically around 500-600 ohms max at 24V).
• What is the formula to convert the mA reading back to temperature?
  Temperature = [(Current - 4) / 16] * 250 - 50. (Where Current is in mA, and the result is in °C).
• Why is my reading stuck at 4mA?
  4mA represents -50°C. If it's stuck here at room temperature, check your wiring polarity, ensure the PT100 is connected properly, or verify the zero calibration potentiometer hasn't been turned all the way down.
• Is this isolated?
  Standard budget transmitters are usually non-isolated. If you require strict galvanic isolation between the sensor and the loop, you may need a higher-tier isolating transmitter.
• What is cold junction compensation, and does this have it?
  Cold junction compensation is for Thermocouples, not RTDs. PT100s do not require cold junction compensation, so it is not a factor for this module.