Why Use a Temperature Transmitter?
The days of temperature transmitters only utilizing an analog signal are behind us. The evolution of technology, in particular, the microchip, has made it possible to create devices that are not only compact but also digital. No longer does it take a screwdriver and multi-meter to communicate with the temperature measurement device. Now it’s possible to hook up a laptop or tablet via a wired connection or wirelessly to get all the necessary temperature data from the transmitter.
A transmitter translates the signals from the temperature probe into accessible and actionable data for the technician. This data helps to optimize the process because changes can be quickly noted, and adjustments can be made to keep material flowing through the processing facility.
Let’s delve deeper into transmitters to learn more about the challenges of wired-direct installations, the purpose and advantages of transmitters, and the most current transmitter features, capabilities and onboard diagnostics available today.
The challenges of wired-direct installations
Historically, some users have preferred to implement wired-direct installations where they connect a thermocouple or RTD directly to a control system input without the use of a transmitter. While this may look prudent on the surface, this approach can add cost, complicate the installation and impact the performance of the measurement point. For example, the cabling from the sensor to the control system input card must match the sensor when wiring direct for the entire run of wiring. This can be costly, as sensor wiring is usually more expensive than standard copper wiring used with a transmitter installation. Wiring direct also has an impact on any changes done in the field. Changing a sensor type in the field requires changing the sensor and the entirety of the sensor wire run to match the new sensor type.
From a performance perspective, the small amplitude signal generated from a wired-direct thermocouple or RTD is susceptible to electrical interference, which can result in inaccurate measurements and possible process shutdown. Wired direct installations also lack any predictive diagnostics to minimize the effects of sensor degradation, resulting in a higher likelihood of unplanned shutdowns or other adverse impacts to the process.
The advantages of using transmitters
A transmitter offers a significant advantage over a wired-direct setup. Aside from reduced drafting time and wiring needs, a transmitter, sensor and thermowell assembly can be set to meet a specific performance goal, which can be arranged through a single vendor.
A temperature transmitter installation’s accuracy and performance are typically better than its wired-direct temperature counterpart due to it being far less susceptible to EMI and RFI interference. Low-level sensors tend to be highly vulnerable to EMI and RFI, particularly in cases where the extension cables act as antennas for noise signals. Transmitters can also filter out environmental noise and compensate for inaccuracies caused by corroded terminations and frayed wiring.
Higher performance is also possible with a transmitter-sensor assembly calibrated for specific performance goals and which better supports custody transfer and safety-related applications.
Wired-direct installations can also leave you prone to unexpected failures with minimal diagnostics coverage. Degraded or broken elements, loose or open connections, moisture in housings, frayed or damaged wiring, and electrical noise can all create risks for maintaining an accurate reading and keeping your process up and running.
Temperature transmitter diagnostics help you avoid measurement failure and process shutdown by identifying failing or degrading sensors and connections by monitoring and evaluating sensor loop resistance and sensor signal noise.
Transmitter features, capabilities and diagnostics
The Emerson Rosemount temperature measurement transmitters feature industry-leading accuracy, stability, and reliability with technological innovations to satisfy your temperature measurement needs.
- Dual Compartment housing with HART®, WirelessHART®, or FOUNDATION™ Fieldbus output
- Dual input capability with advanced diagnostics suite, including Hot Backup™, sensor drift alert, thermocouple degradation and min/max logging
- Integral Transient protection, 5-year stability, SIL 2 certification
- Large LCD display
Each feature is designed to make the transmitter easy to operate and reliable.
Of particular interest are the advanced diagnostics that allow an operator to troubleshoot the temperature probe or determine transmitter health.
In our upcoming third blog post in this series on temperature measurement, we’ll delve into thermowell basics, including the calculations needed to size them for an application and how the Rosemount Thermowell Design Accelerator can significantly simplify the thermowell design process.
In the meantime, download The Engineer’s Guide to Industrial Temperature Measurement, 2022 Edition, to learn everything you need to know about these temperature components.