Application Scenarios:
In a commercial building’s HVAC system, the temperature of chilled water supplied to air-handling units must be precisely controlled for energy efficiency and comfort. A Pt100 sensor is installed in the chilled water pipeline. The ABB TP867 transmitter, mounted in a nearby electrical cabinet, is connected to this sensor. It powers the Pt100. measures its resistance change with temperature, and converts this into a proportional 4-20mA current loop signal. This signal is then wired to the building management system’s (BMS) analog input module hundreds of meters away. The BMS uses this precise reading (e.g., 12mA representing 8°C) to modulate the cooling valves, ensuring optimal system performance. The TP867’s two-wire design simplifies installation, and its high accuracy ensures the control loop operates efficiently, saving energy.
Technical Principles and Innovative Values:
The ABB TP867 embodies the principle of robust signal conditioning, transforming a small, noise-sensitive resistance signal into a robust industry-standard current signal.
Innovation Point 1: True Two-Wire, Loop-Powered Simplicity. Its core value is the elimination of a separate power cable. The unit is powered directly by the same 4-20mA loop that carries its output signal. This drastically reduces wiring costs, simplifies intrinsic safety (Ex i) applications when used with an associated safety barrier, and minimizes installation errors. The low power consumption allows operation with standard 24V DC supplies.
Innovation Point 2: High Accuracy and Advanced Linearization. The transmitter features precise signal conditioning circuitry with advanced linearization algorithms, especially for RTDs like Pt100. The RTD’s resistance-temperature relationship is not perfectly linear. The TP867 applies correction to provide a linear 4-20mA output directly proportional to temperature, ensuring high measurement fidelity for the control system without requiring additional software linearization.
Innovation Point 3: Flexible Configuration and Diagnostics. Despite its compact size, it offers flexible configuration. Users can typically set the input type (e.g., Pt100 3-wire), measurement range, and damping via DIP switches or potentiometers without needing a PC. Some models feature diagnostic capabilities, such as outputting a signal outside the 4-20mA range (e.g., 3.8mA or 22mA) to indicate sensor burnout (open circuit) or other faults, providing early warning to the control system.
Application Cases and Industry Value:
Case Study: Improving Batch Consistency in a Food Processing Plant.
A sauce and dressing manufacturer had issues with batch consistency because the temperature readings from multiple steam-jacketed kettles were unreliable. The long sensor wires picked up electrical noise from variable frequency drives (VFDs) controlling agitators, leading to fluctuating readings in the PLC. They replaced direct sensor wiring with ABB TP867 transmitters mounted locally at each kettle.
Each kettle’s Pt100 sensor was now connected to a TP867 just a few meters away. The transmitter converted the signal to a noise-immune 4-20mA current loop. The plant engineer noted: “The TP867s were a game-changer. The noisy, millivolt-level signals are now robust 4-20mA signals. Our temperature control is now rock solid. We eliminated batch variations due to false readings, improved product quality consistency, and reduced ingredient waste. The DIN-rail mounting made installation in our crowded panels easy, and the simple range setting got us up and running quickly.”
Related Product Combination Solutions:
Pt100 RTD Temperature Sensors: The most common sensor input for the TP867 (e.g., 3-wire configuration for highest accuracy).
ABB CP-S Series Power Supplies: Provide stable 24V DC loop power for the transmitter network.
PLC/DCS/Controller with Analog Input (AI) Cards: The destination for the 4-20mA signal (e.g., Siemens SM331. Rockwell 1756-IF8).
Signal Conditioner/Isolator (e.g., ABB CM-ENS): For applications requiring additional signal isolation or distribution to multiple systems.
DIN-rail Mounted Enclosure: To house and protect the TP867 and associated terminal blocks.
HART Communicator/Software: For advanced models that support HART protocol, enabling digital configuration and diagnostics from the 4-20mA loop.
Intrinsic Safety (IS) Barrier (e.g., MTL778+): Required for installing the transmitter and sensor in a hazardous area (Zone 0/1), as the TP867’s two-wire design is ideal for this architecture.
Temperature Gauge/Indicator with 4-20mA Input: For local temperature display connected to the transmitter’s output.
Installation, Maintenance, and Full-Cycle Support:
Installation of the ABB TP867 is straightforward for electricians. The unit snaps onto a standard 35mm DIN rail inside a control panel or junction box near the process. Wiring involves: connecting the RTD sensor wires to the input terminals (observing 2. 3. or 4-wire configuration), and connecting the 4-20mA output loop (loop power +, transmitter +, transmitter -, loop return) to the power supply and control system. Configuration is done via onboard DIP switches to match the sensor type and desired range. An accurate digital multimeter is needed to calibrate the zero and span potentiometers if fine-tuning is required.
Once commissioned, the transmitter is virtually maintenance-free. The primary maintenance task is verifying the loop current against a known temperature or a simulated resistance input. Any drift or fault is usually indicated by the control system reading an out-of-range value. Our support ensures you get the most from this reliable workhorse. We provide detailed datasheets and wiring diagrams, assist with sensor selection and range configuration, and supply genuine replacement units. We are committed to helping you build stable and accurate temperature measurement loops.
Contact us for a customized solution to implement reliable, loop-powered temperature measurement for your process control system.
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