Temperature is the most commonly measured parameter in commercial and industrial settings. The temperature sensor of choice in these environments is usually a thermocouple or resistance thermometer such as an RTD or PRT. These temperature sensors share many of the same benefits: a wide measuring range; good accuracy; and a simple, reliable design. They also share a disadvantage: the signal they generate is occasionally not adequate for temperature control systems. Temperature transmitters and transducers are used to mitigate this shortcoming.
When Temperature Transmitters / Transducers are Necessary
The simplest temperature control or measurement system is a single sensor, either a thermocouple or RTD, wired directly to a controller, display, or recorder/data logger. This system works fine if it includes just a single sensor and if the distance between sensor and the measurement/control device is short. Any system more sophisticated than this requires a temperature transmitter or transducer.
Temperature transmitters and transducers provides the interface between sensor(s) and the measurement/control device. Temperature sensors; unlike pressure, level, flow or others; generate a non-linear millivolt signal. If that signal has to travel too far—say, over 100 feet—the increased resistance it faces as it travels down the wire can distort the weak signal causing inaccuracy.
Temperature transmitters convert the non-linear millivolt signal to a linear milliamp or voltage signal which can be sent over longer distances without the signal degrading. They have the added benefit of providing a platform upon which a digital signal like HART or Fieldbus can be piggybacked allowing for highly sophisticated communications and control. Transmitters and transducers also allow multiple sensors to be incorporated into a single temperature control/measurement system.
Types of Temperature Transmitters / Transducers
Temperature transmitters and transducers can range from simple devices installed between the sensor and the controller, display, or recorder/data logger to much more complex instruments that isolate, amplify, and filter signals and may include a range of communications or other options.
Ignoring for a moment the more sophisticated models which are designed according to individual manufacturer’s specifications, temperature transmitters and transducers can be divided into two “types” which reflect their mounting style.
Temperature transmitters and transducers can be either DIN rail or In-head mounted. When mounted on a DIN rail, the transmitter sits next to the measurement/control device. With in-head mounting, the transmitter is mounted inside a connection head that’s part of the sensor assembly. The mounting style best for you depends on the specifics of your application.
Things to Consider When Selecting a Temperature Transmitter / Transducer
- What is the distance between the sensor(s) and the measurement/control device?
- How many sensor are used in the loop?
- Do digital communications or other options need to be supported?
- Does the transmitter require loop power? If so, how is it supplied?
- Does the transmitter need to be intrinsically safe, isolated, or require any other approvals?
- Remember: since the transmitter converts the signal from the sensor, the new signal will have to be rescaled at the measurement/control device.
If you have any questions regarding temperature transmitters / transducers please don't hesitate to speak with one of our engineers by e-mailing us at sales@instrumart.com or calling 1-800-884-4967.
