How’'s your conditioning?

The key to control is accuracy, both in measurement and in signal conditioning. Noise caused by ground loops can cause minor to severe signal degradation.

By Loren Shaum, contributing editor

Much like physical  conditioning is important to keep yourself in shape, signal conditioning is important to ensure correct information is transmitted. If signals from various sensors or transducers are not conditioned properly, inaccurate information is sent to a controller and/or to a network, potentially with catastrophic effect.

Regardless of sensor types, proper signal conditioning is essential to assure proper control and to deliver correct information to a network. Wireless technology only heightens the need for signal conditioning.

“As wireless technologies such as Wi-Fi and ZigBee continue to develop and gain adoption for data acquisition, more and more applications for remote acquisition and logging can now be addressed,” says Swapnil Padhye, data acquisition product marketing engineer at National Instruments. “These new areas span across a wide range. Very similar to the case of cabled data acquisition, reading from sensors like humidity, temperature, and flow remains an important step in these wireless applications. Providing the right type of signal conditioning for sensors enables the most accurate measurements and it continues to be a critical component of wireless data acquisition.”

Let’s take a look at the key conditioning functions of the sensor signal configuration.

Amplification

Thermocouple signals come to mind as one of the more sensitive, low-level signals needing amplification to create accurate transmittable signals. Omega Engineering supplies a variety of thermocouple signal conditioners, including the iD Series where thermocouple inputs are amplified, often filtered, and then delivered to a receiver device. To deliver thermocouple temperature measurement data to a network, the iDRX series provides a RS-485 output.

Isolation

Isolation provides immunity to dangerous and/or degrading effects of noise, transient power surges, internal ground loops, and other hazards present in industrial environments. Dataforth offers a family of isolated signal conditioners. The SensorLex 8B conditioners are configured for voltage, current, temperature, position, frequency, and strain measuring devices. Conditioning includes linearity, amplification, filtering, and 1,500 Vrms isolation.

Pulse Shaping

Pulse shaping might be required because a limited number of sensors or transducers implement a pulse-code data or frequency output. The Ultra SlimPak II from Eurotherm-Action Instruments is an example of a frequency conditioner. These offer lower power usage, improved accuracy and an optional e-mail notification of alarms. Allowable input frequencies are up to 10 kHz. Input amplitude can range from 150 mV to 150 Vrms.

Universal Signal Conditioners

“There are many instances when signal conditioning is an appropriate solution,” says Robert Schosker, product manager at Pepperl+Fuchs. “Thermocouples or RTDs might require conversion to any of several standard instrument signals.” Schosker notes that the key to control is accuracy, both in measurement and signal conditioning. Noise from ground loops can cause signal degradation. Signal conditioners will provide the needed isolation, amplification, filtering, and linearity corrections to eliminate the ground loops.

Dan Jacobsmeyer, FlexConnect product specialist at Emerson Process Management, works with Emerson offices around the world to migrate legacy distributed control systems to its DeltaV DCS platform. “FlexConnect sells cable-only solutions, as well as cable and signal-conditioning circuit boards to allow direct connection from the legacy DCS to DeltaV,” says Jacobsmeyer. “I evaluated P+F’s KFU8-USC-1.D modules for use in migration projects where the field signals are not compatible with DeltaV. Some equipment has voltage offsets or leakage to ground. A universal signal conditioner frequently is needed to condition the field signal to work with a DeltaV card already installed in the system.” 

 

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