Types of Signal Converters Commonly used in Industrial Control

Signal converters change a signal from one form to another. In most cases, we have standard inputs and output ranges.

Most signal converters have two adjustments-zero and range.

Examples of Signal converters

Nozzle-flapper and differential pressure cells

The nozzle-flapper system is widely used in D.P. Cells. An example is shown below, that converts differential pressure (e.g. from a differential Pressure flow meter into a standard pneumatic signal). This is widely used in the control of air operated pipeline valves.

The bellows respond to the differential pressure and moves the lever. This moves the flapper towards or a way from the nozzle. The air supply passes through a restrictor and leaks out of the nozzle. The output pressure hence depends on how close the flapper is to the end of the nozzle. The range of the instrument is adjusted by moving the pivot and zero position is adjusted by moving the relative position of the flapper and nozzle. This system is used in a variety of forms. Instead of bellows, a bourdon tube might be used and this is operated by an expansion type temperature sensor to produce a temperature-pneumatic signal converter.

You can also read: Types of Proximity Sensors used in Industrial Control

Current/Pressure conversion 

The figures below show typical units for converting 4-20 mA into 0.2-1 bar or 3-15 psi. They contain adjustments for range and zero. They are widely used for converting the standard pneumatic and electric signals back and forth. They can also be adjusted to work with non standard inputs to convert them into a standard form.

Current to Pressure Converter

Pressure to Current Converter

Electric D.P. Cells

They provide the same functions as the pneumatic versions but they are given an output of 4-20 mA using electrical pressure transducers. They are typically used with D.P. Flow meters.

Differential Pressure Transmitter

Analogue -Digital Converters

Analogue to digital conversion is a process of turning an analogue voltage or current into a digital pattern which can read by a computer and processed, this is done by analogue -digital converters.  Lets look at the Binary Numbers, a number may be represented in digital form by simply setting a pattern of voltages on a line high or low. It is normal to use 4, 8, 16 or 32 lines. An 8 bit binary pattern is shown in the below figure:

The total pattern is called a word and the one above is an 8 bit word. The pattern may be stored in an 8 bit register. A register is a temporary store where the word may be manipulated. The Bit zero is called the least significant bit (LSB) and the bit with highest value is called the most significant bit (MSB). Each bit has a value of zero when off (LOW) or the value shown when on (HIGH). The maximum value for an 8 bit word is 255.

Digital to Analogue Converters

These are devices for converting a binary number into an analogue voltage. The change in the binary value from zero to a maximum corresponds with a change in the analogue value from 0 to maximum.

One of the manufacturers of signal converters is Omega.

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