In this post, we will discuss the process indicator. Process indicator is an important instrument and very useful in instrumentation and control. this post will also help you to face an interview.
As the Name Indicates Process Indicator is made from two words.
Process & Indicator, Indicator means a device or instrument used to indicate some parameters. So Process Indicator is an instrument used to indicate the process parameters.
The Process parameters are the parameters we use in our process. Process parameters Example- Pressure, Temperature, Flow, Level, pH, and others.
To indicate these parameters, we need to measure these parameters.
How we measure these parameters-
To measure these parameters, we will use different transmitters and sensors.
To measure Pressure, we use Pressure Transmitters. The supply for Pressure Transmitter is 24 Volts DC Supply. The output given by the pressure transmitter is 4-20 m Amperes(Normally used).
To measure Differential pressure, we use differential Pressure transmitter.
To measure temperature, we use a Resistance Temperature Detector (RTD) and Thermocouples. The output given by RTD is Resistance and the output given by Thermocouple is Millivolts.
To measure flow, we use flow transmitters and flow meters. The output given by the flow transmitter is 4-20 m Amperes. The output given by Flowmeters is also 4-20 m Amperes.
To measure Level, we use Level transmitter and ultrasonic level transmitter. The output given by the level transmitter is 4-20 m Amperes.
Similarly, Different sensors are used to measure different Process Parameters.
The output given by the measuring instruments is given to process indicators. It becomes the input for the process indicators.
Process indicators are categorized into two categories according to inputs indicated-
- Single Input
- Universal Input
As it is clear from the name itself that single input Process Indicators accept only single input and indicate it.
It means, that we can use the single input process indicators to indicate the single process parameter. So we can use it to indicate only one from Resistance, Millivolt, and m Amperes.
The universal input Process indicators are used to indicate more than one inputs and these indicators are used to indicate all the inputs, so we call these indicators the universal input indicators.
At a time the universal input indicator shows one input but we have the option to choose the different input to indicate.
In the universal input process indicator and single input indicator, RTD, Thermocouples and m Amperes symbols will be given so that we can connect them accordingly.
So the advantage of universal input indicators over single input indicators is that the universal input indicators are not restricted to indicate only single input.
Another advantage of using the universal input indicator is that suppose we are using it to indicate the temperature but we want to indicate the pressure now, so it can be used by changing its input.
So one thing is clear from the above discussion that if we want to use the universal indicator for indicating one quantity to other, we will need to change the input of the process indicator.
It is clear from the above image that if we are using RTD, we will connect at terminal 1,2 and 3. short-circuited wires (same colour wires) at terminal 1 and 2 and the common wire (Different colour wire) will connect at terminal 3.
For connecting thermocouple, we will use terminal 2 and 3. terminal 2 will be for positive wire and terminal 3 will be for negative wire.
m Amperes Connection :
For connecting m Amperes, we will use terminal 3 and 4. terminal 4 will be for positive wire and terminal 3 will be for negative wire.
For making selection of input, we will use programming switch.
after selecting the programming switch, we will select the input from programming. In some process indicators, this programming switch is not given so we will select the input from programming.
It is easy to change the input of a process indicator, for this we can go through the manual of that process indicator if we don’t have the manual we can search online on any search engine for the manual of process indicator by the manufacturing company and model number of that process indicator.
Questions from the topic Process Indicator
What is the use of process indicators?
What are the different types of process indicators?
Define Process Parameters?
How can we measure the Process Parameters?
Define universal input process indicator?
If we want to use temperature control valve as a pressure control valve what changes we need to do at our indicator side?
if you will answer the questions, it will be a good practice for you.
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