The ABB 691HT is a high-performance, head-mounted temperature transmitter designed to convert sensor inputs into a standardized 4–20 mA signal with integrated HART protocol communication. It is engineered to provide high accuracy and reliability in harsh industrial environments. By utilizing HART, this transmitter allows for digital remote configuration, diagnostics, and process variable monitoring, making it an essential tool for modernizing legacy temperature measurement loops.
📋 Product Specifications
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Series: 691 Series Temperature Transmitter
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Part Number: 691HTME0000000
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Input: Universal (RTD, Thermocouples, mV, and Ohm)
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Output: 4–20 mA DC with HART Protocol
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Mounting: Head-mounted (Standard connection heads)
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Accuracy: High-precision signal linearization
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Operating Temperature: -40°C to +85°C
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Dimensions: 44 mm diameter x 24 mm height (approximate)
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Weight: 0.05 kg
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Country of Origin: Italy / Germany
🌐 Application Fields
This transmitter is widely used in process industries including Oil & Gas, Chemical, Food & Beverage, and Power Generation. Its primary application is to transmit precise temperature data from field sensors (such as PT100 RTDs or Type K thermocouples) to a DCS or PLC. The HART capability is particularly valuable in remote or hazardous locations where manual adjustments to the transmitter would be difficult or unsafe.
🛠️ Product Usage Instructions
Installation involves mounting the transmitter within a standard DIN B connection head. Ensure the sensor probes are wired to the input terminals following the correct color code. Connect the 4–20 mA loop to the output terminals, ensuring the loop resistance is within the operating limits (typically 250 ohms to 1100 ohms for HART communication). Once powered, use a HART communicator or software (such as ABB’s Asset Vision) to configure the sensor type, range, and unit settings. The status LED will verify successful initialization and communication status.
❓ Frequently Asked Questions
Q: What is the benefit of HART protocol in the 691HT? A: HART (Highway Addressable Remote Transducer) allows you to perform remote diagnostics, calibrate the device without disconnecting wires, and transmit extra process data (such as sensor health or ambient temperature) alongside the primary 4–20 mA control signal.
Q: Can I use this transmitter with different types of sensors? A: Yes, the 691HT is a universal transmitter. You can configure it for various RTDs (2, 3, or 4-wire) and multiple thermocouple types through the digital configuration interface.
Q: How do I troubleshoot a HART communication error? A: Ensure your HART modem is connected in parallel with the 4–20 mA loop. Check that the loop resistance is at least 250 ohms; if the resistance is too low, the HART signal cannot propagate. Also, ensure the transmitter is powered within the required 10.5V–45V DC range.
Q: Is this transmitter suitable for hazardous areas? A: The 691HT is typically designed with Intrinsic Safety (IS) options. Always verify the specific approval markings (ATEX/IECEx) on the device label before installing it in an explosive atmosphere to ensure it meets your plant’s safety standards.
