INOR was founded in 1939 in Sweden and is one of the world’s leading manufacturers of signal conditioners with a focus on temperature transmitters. In 1974, INOR introduced the world’s first head-mounted temperature transmitter which inspired a new era in industrial temperature measurement.

Novus was founded in 1982 in Brazil and have commercial offices all over the world. Specialists in data acquisition and single loop control, their products are welcomed as an industry standard. Through consistent product development Novus’ range has expanded to include controllers, temperature and humidity sensors and transmitters, pressure transmitters and data loggers.

Drago, based in Germany has been manufacturing and supplying high quality signal converters since 2002. Drago specialize in particularly durable and reliable components for automation technology, both for the standard sector and for unique applications. Their range of DIN rail devices is vast, and includes a 6mm narrow modular case series for preserving space in the cabinet.

4-20mA

4-20mA transmitters first appeared in 1950’s as a replacement of pneumatic control systems which were typically found throughout a plant at the time.

The greatest advantage of using a current loop for signal transmission is the loops low sensitivity to electrical noise as it is a generally low impedance system, which is important for long distance transmission in harsh industrial environments.

Because the accuracy of the signal is not affected by the voltage drop in interconnecting wiring, the current loop is virtually ‘lossless’. In this manner and because of Kirchoffs Current Law, the plant can be assured that if the receiver indicates 12mA, you can be certain that 12mA is passing through the transmitter.

0-10V

0-10V transmitters (or in some cases 0-5V) use voltage to represent a variable signal, rather than current as with the 4-20mA transmitters. It is a simple method of signal transmission commonly used in HVAC applications, but is has some inherent disadvantages.

The most important disadvantage is that it is susceptible to electrical interference. Devices such as motors, relays and noisy power supplies can induce voltages onto signal lines that can degrade the 0-10V sensor signal. The 0-10V signal is also susceptible to voltage drops caused by wire resistance, especially over long cable runs resulting in inaccurate signals.

Sensor faults cannot be detected as well, meaning a value of 0V can indicate either a zero value or there is no signal. 2-10V or 1-5V transmitters avoid this issue, but are not as commonly found.

Further Reading

• What is a transmitter?
• Why use transmitters?
• Why use isolated transmitters?