Consider the Lifecycle Costs

While there is a lot of added functionality available in today’s temperature transmitter technologies, it does not come without a price. However, suppliers make the case that a feature-rich temperature transmitter will generally pay for itself many times over during the course of its operation.

“Often a customer will specify a lower-tiered temperature transmitter based solely on price considerations,” says Patrick Cupo, marketing manager for pressure and temperature products at Invensys Process Systems (www.ips.invensys.com). “After a few months of operation, he regrets not purchasing a higher-tiered product. The higher-tiered product had the one diagnostic he needed to prevent the unplanned shutdown. The cost of the shutdown exceeded the additional cost of the higher-tiered temperature transmitter.”

To prevent such a scenario, Cupo says users should have a clear understanding of their temperature measurement requirements, including whether or not the application calls for monitoring or control, the necessary accuracy, safety issues, etc. “What are the consequences of the temperature measurement being off by three or four degrees?” asks Cupo. “Do I lose an entire batch? Do I no longer comply with an agency requirement? Are there safety issues?”

Specification & Installation Best Practices

The installation of modern-day temperature transmitters, while relatively simple, does require a mindful approach, according to Siemens’s Cushing. Two key characteristics Cushing recommends users consider are the physical size of the transmitter and the mounting type. He says users will on occasion purchase a transmitter without considering whether or not it will actually fit in the space in which they would like to install it. Meanwhile, regarding mounting, Cushing says users can typically choose between head-mount, rail-mount and field-mount devices. He says head-mount devices offer simplicity and low cost, while field-mount devices are typically a good fit for applications that involve high temperature and/or require a remote option.

In addition, Cushing says users should keep in mind the wiring requirements of their temperature measurement application. If the transmitter is a low-end device, for example, it may not have the proper RFI protection to prevent noise from interfering with the signal transmission.

Emerson’s Engelstad says users should also try to install their temperature transmitter as close to their sensors as possible to reduce the lead lengths of the sensor signal. In doing so, users can limit the potential for noise interference, as the low-level sensor signal will have a shorter distance to travel to the transmitter before it is converted into a high-level digital signal.

“If you can eliminate longer lead lengths from your sensors, that can make a big difference from a performance perspective,” says Engelstad.