Hi friends, I hope all of you are fine. As you already know we have started a series of PLC articles. In last lecture, we discussed detailed article on plc discrete inputs and outputs. In today’s tutorial, I am going to explain to you about detailed article on analog input and output devices of plc.
Previous PLC controllers were restricted to distinct or digital input and output interfacings, which permitted merely on or off category instruments to be linked with a controller. This restriction intended that the PLC controllers could have only fractional governing of numerous processes submissions. Nowadays, still, a whole assortment of both separate and analog interfacing is accessible which will permit controller to link with any kind of process. So let’s get started with Analog Input and Output Devices of PLC.
Analog Input and Output Devices of PLC
- Previous PLC controllers were restricted to distinct or digital input and output interfacings, which permitted merely on or off category components to attached with plc.
- Discrete inputs and outputs work only for two conditions the first one is on and the second one is off.
- In association, analog components define such physical quantities (these are qualities of any substance defined by some calculations) that has large no of numerical values.
- Analog input/outputs differ from zero to twenty mA milliamps, four to twenty mA, or zero to ten volts.
- The given diagram shows how PLC analog input/output components are used in gaging and exhibiting the level of liquid in a container.
- The analog input interfacing unit comprises the electric circuit essential to receive an analog voltage/current signal from the level spreader field component.
- This input is transformed from an analog to a numerical assessment for the usage of the CPU.
- The circuit of the analog output unit receives the numerical assessment from the CPU and changes it again to an analog signal which enterprises the field container level measuring device.
- Analog input units usually have numerous input stations that permit four, eight, or sixteen components to be linked with the PLC.
- There are two main kinds of analog input units voltage detecting and current detecting.
- Analog sensing device calculate the variable physical magnitude above a precise assortment and produce a resultant voltage/current signal.
- The physical quantities that can easily be calculated by the plc analog unit are temperature, force, mass, distance, velocity, level.
- For instance, a sensing device can calculate temperature above a range of zero to five hundred Celsius, and output an analogous voltage signal which differs among zero and fifty millivolts.
Plc Temperature Measuring Analog Module
- The given diagram shows the example of a voltage detecting input analog unit used to calculate temperature.
- The assembly figure relates to a four-channel analog thermocouple input unit.
- A variable direct current (DC) voltage whose value in some mV is directly proportional to the temperature whose value is found, are produced by the thermocouple.
- This voltage is augmented and convert to digits by the analog input unit and then directed to the CPU on command from a program order.
- Due to the less value voltage input signal, a wound protected couple of wire is used in cabling the circuitry to decrease unsolicited electrical sound signals which can occur in the conductive wiring from another cabling.
- When we are working on a thermocouple which is not connected with the ground, the protection circuitry should be linked with the ground at the unit finishing points.
- To get precise interpretations from each of the stations, the temperature among the thermocouple cable and the input network should be recompensed for.
- A (CJC) thermistor is combined with the casing of the unit for this function. Analog to digital conversion is done by the (A/D) converter, which is the main part of analog input unit.
- Analog voltage input units are offered in two categories first one is unipolar and the second one is bipolar.
- Unipolar units can receive an input signal that has positive values. For instance, if the field component outputs are zero volts to one-ten volts, then the unipolar units will be cast-off.
- Bipolar signals fluctuate among an extreme negative point and an extreme positive point.
- For instance, if the field components outputs are minus ten Volts to plus ten Volts a bipolar unit will be cast-off.
- The tenacity (resolution) of an analog input network states to the minimum alteration in input signal assessment which can be detected and is founded on the number of bits used in the numerical demonstration.
- Analog input units should generate a sort of numerical values among an extreme and least value to signify the analog signal above its complete extent.
Applications of Analog Input and Output Devices of PLC
- The given diagram explains the practical implementation of the analog input and outputs of devices in the programmable controller logic network.
- In given circuitry plc regulate the quantity of liquid in the tank by varying the control valve slowly.
- The movement of liquid is governed by the analog output by controlling the valve.
- First, the valve is open completely so the liquid in tank reaches a set point, to obtain a set value processor of plc send a signal to output for the required level of liquid.
I also have uploaded some related articles to plc you read them for further learning.
- Introduction to PLC
- Working of PLC
- Parts of PLC
- Input and Output Section of PLC
- PLC Discrete Input and Output Devices
That is the complete tutorial about analog inputs and output of PLC if you want to know further or have some suggestions for the improvement of this article can ask in comments. See you in the next tutorial PLC Special Inputs and Outputs.