MTL Barries - MTL5573 TEMPERATURE CONVERTER (THC or RTD input)

The MTL5573 is a temperature converter that converts a low-level DC signal from a temperature sensor in a hazardous area into a standard 4-20mA current signal for a safe-area load. Its working principle involves receiving a signal from a thermocouple (THC) or a resistance temperature detector (RTD) in a hazardous location, processing that signal through internal linearization and ranging, and then transmitting a proportional 4-20mA output signal to a control system in a safe location. This is an isolated device, meaning it electrically separates the hazardous and safe areas to prevent ignition..

Working principle

• Input: The device accepts low-level DC signals from temperature sensors like thermocouples (Types J, K, T, E, R, S, B, N) or RTDs (2, 3, or 4-wire) in a hazardous area.
• Processing: It uses software-based configuration to linearize the sensor signal, which is then scaled to match the desired input and output ranges.
• Isolation: The MTL5573 provides intrinsic safety by electrically isolating the hazardous area circuits from the safe area circuits. This prevents any stray electrical energy from the safe area from igniting a flammable atmosphere in the hazardous area.
• Output: The processed and isolated signal is converted into a 4-20mA current output, which is a common industrial standard.
• Load Drive: This 4-20mA signal can drive a load, such as a recorder or a control system, located in the safe area.
• Power: It is powered by a 20-35 VDC supply in the safe area and operates as a one-channel device.
• Configuration: The specific function, ranging, and other parameters are configured using a personal computer and a special software program.

The MTL5573 is a single-channel, intrinsically safe temperature converter and isolating interface used to connect temperature sensors in a hazardous area to control systems in a safe area. Its core working principle is based on galvanic isolation to ensure safety while converting the sensor signal into a standard process current signal.

Working Principle

The MTL5573 performs several key functions as part of a process control loop:

1. Signal Input (Hazardous Area): The module accepts low-level DC signals from various temperature sensors (thermocouples (THCs) or 2-, 3-, or 4-wire RTDs) located in a hazardous or potentially explosive environment. Terminals in the hazardous area are designed to be intrinsically safe, limiting the amount of energy (voltage and current) that can enter the area, thus preventing ignition of flammable gases or dusts.
2. Signal Conversion and Processing: The low-level sensor signal is passed through the module's internal circuitry. This involves:

• Linearisation and Ranging: The non-linear input from the sensor is conditioned and converted into a linear value representing the actual temperature. The specific range and sensor type are configured using a personal computer with special software (MTL PCS45).
• Cold Junction Compensation (CJC): For thermocouple inputs, an integral CJC sensor compensates for the temperature variations at the terminal connections.

3. Galvanic Isolation: This is a crucial safety feature. Internal transformers or similar mechanisms provide a complete electrical break between the hazardous area circuitry and the safe area circuitry. This eliminates the need for a high-integrity earth connection (often required by simpler zener barriers) and prevents ground-loop problems, simplifying installation.
4. Signal Output (Safe Area): The processed and isolated signal is converted into a standard 4/20mA current output. This current loop signal is robust and drives the load in the safe-area equipment, such as a PLC, DCS, or display unit.
5. Monitoring and Safety: The module also includes features for monitoring sensor failure (e.g., upscale or downscale drive on burnout) and provides alarm indications via an LED.

In essence, the MTL5573 acts as a bridge, ensuring that the necessary electrical signals can pass between different areas of a plant safely, without compromising the explosion protection integrity of the hazardous zone.

 Full Datasheet