Typical signal conditioner techniques

[GMI]

Originally published on GMI blog by GM International | July 30, 2020

Signal conditioners isolate, supply, amplify, normalize and convert various electric, mechanic, chemical signals in standard signals for data acquisition systems.

Signal conditioning is an electronic technique aimed at solving problems that arise when interfacing sensors with control units. This is needed because sensor’s output signals do not all share the same electric nature (current, voltage, resistance, etc.), or typology (for example alternate, direct or pulsing current).

Signal conditioners (converters) can be installed in electric panels, on sensors or actuators or controllers, integrated in A/D (Analogical/Digital) conversion boards and in multiplexing systems. Below we are going to review some conditioning techniques implemented in G.M. International Series D1000 & D5000.

It should be highlighted that GMI conditioners, apart from their converting functions, are also capable of operating in hazardous areas, galvanically isolating the signal loops. Other output options are also available for communicating via Hart, Modbus, offering flexibility to fit all applications in the market.

Current, voltage and frequency converters

Typically, in process and factory automation, input signal needs to be converted to a normalized signal (4-20 mA or 0-10 V for example) on the output. Additionally, it is crucial to have the correct conditioner-equipment to isolate, amplify, linearize and convert any signal from low-level sensors in order to transmit without any voltage drop even for long distances.

In factory automation, common ground connections should always be avoided since presence of multiple and different loads, all of them being connected to ground.

Another problem may be caused by the noise present in almost all industries. Solutions to this and other normalization problems are provided by analogic, digital, serial, pulse and frequency converters-conditioners-repeaters.

Trip amplifiers

Trip amplifiers are digital signal converters or analogic signal conditioners (current, voltage, temperature) based on independent amplifiers, where output signal can be direct or reverse. Alarms activate or deactivate a relay or transistor with the following functions: high-alarm, low-alarm or burnout.

The activation or deactivation of any relay can be configurable within all the input signal range.

Typically, such devices supply stabilized power to transducers with short-circuit protection and allow configuration of alarm set-points, delay and hysteresis.

Load cell and vibration transducers

Measures based on strain gauge bridges, such as weight, vibration, torque and force are other very common conditioning techniques. Typically, the weight of the external measuring bridge is read by the signal conditioner and converted into a normalized analog signal.

Bridge measure-converters process millivolt input signals. In applications such as industrial weighing, load cells under “measure bridge” produce a voltage signal which is amplified, isolated and converted in one linear voltage or continuous current output.

Temperature Converters

Whenever a resistance measure depends on temperature, a current of a few milliAmps is injected from a source of constant current to a signal converter. In order to take voltage drops into account, voltage drop on the return cable is measured and its value is multiplied by two. 

If thermocouples are used instead, a thermal-voltage is present on the terminal blocks of the converter, because of the difference between the cable’s and the conductive bar’s material. To compensate the consequential alteration of the measure, temperature is measured close to the terminal blocks of the converter. The signal converter calculates the final measure, basing on the value at the terminal blocks. This technique is known as “Col Junction Compensation”. 

Signal Repeaters

Inputs received by repeaters are typically transmitted with higher power so propagation can be guaranteed over long distances with low drop. Analog repeaters are used whenever current or voltage analog signals are transmitted. They are also used in junction lines which transmit multiple binary pulse signals through Frequency Division Multiplexing (FDM). Digital repeaters can amplify the signal as well as restoring and synchronizing pulses.

Smoke Detectors

Smoke Detectors represent one of the most important conditioners for people and objects safety. To reduce spurious trips, their installation and use must be configured in conformity to environment conditions.

It is possible to divide detectors basing on their functionality: variation of the electric field due to combustion; reduction of light intensity due to smoke; rise of temperature; smoke movements. Elements such as field display, interfaces, software compatibility; number of relays or transistor output, possibility to use sensor remotely, on-board-diagnostic and other advanced functions offer users other advantages and make a product more suitable than others.

G.M. International signal conditioners

G.M. International offer a wide range of intrinsically safe signal isolators, SIL2 & SIL3 certified, with the D1000 & D5000 series: analogic isolators (D5014S, D5212, D5011, D5020), frequency and digital isolators (D5030, D5031, D5032, D5036, D5037, D5040, D5048, D5049, D5090, D5096), trip amplifier (D5254), signal repeaters (D1061), vibration and strain gauge converters (D5062, D5263, D5264), temperature converters (D1072, D5072, D5273, D1073), smoke detectors (D1022, D1080, D1081, D1180).

[Rodrigo_Garcia]

Thanks!