Advancements in microprocessors and electrical components have led to new ways of monitoring, sensing and communicating important process variables, such as temperature. One advance in the monitoring of this critical metric – the temperature transmitter – is also one of the most widely used devices in the process control industry. A Control Engineering Magazine study found that 92% of respondents indicated they use these instruments to control their processes.
The temperature transmitter combines the technology of the temperature sensor with additional electronics that allow for remote monitoring and configuration of the transmitter parameters.
Selecting a Temperature Transmitter
You should consider these factors when selecting your instrument:
Installation
Start with the environment in which you will install the transmitter. If you have a short distance between the sensor measurement and your control room (and this distance is free of plant electrical interference), then you can install a temperature transmitter in the control room. If you have a long distance between the sensor and the control room (or if plant noise will adversely affect the sensor’s signal), then you should install the instrument as close to the sensor as possible.
Configuration
You can configure available universal temperature transmitters using on-board controls, hand-held configurators, and/or with PC software.
Accuracy
These instruments differ greatly in measurement accuracy, ranging from those that provide accuracies of ±1°F to those that deliver accuracies of ±0.025°F.
Sensors
WIKA can recommend the best sensor for your application – typically a resistance temperature detector (RTD) or a thermocouple. RTDs include a length of fine coiled wire wrapped around a sheathed probe to protect it. The material has a predictable change in resistance as the temperature changes, which allows the sensor to determine a precise temperature measurement. In general, an RTD will give you a more accurate, stable temperature measurement than a thermocouple, if the more fragile RTD can withstand the environment.
RFI/EMI Protection
Always stipulate a transmitter with a stated Radio Frequency Interference (RFI)/ Electromagnetic Interference (EMI) immunity specification. RFI and EMI can diminish transmitter performance and accuracy, and can even cause complete instrument malfunction.
Diagnostic Capabilities
Analog transmitters can provide basic diagnostics, while digital ones can continually monitor the sensor and point you to a broken wire.
Certifications
If you are installing a temperature transmitter in a hazardous area, you need to make sure that you specify an instrument approved for use in that classified area. Look for the coding system that identifies the instrument’s hazardous area rating (e.g., Class I, Division I, Groups A, B, C, D).
Customization
Because you must take many details into consideration when selecting temperature monitoring instrumentation, WIKA’s technical advisors can help you identify and produce the appropriate instrument for your specific application requirements.