To automate any system we need many sensors to control the activity by giving signal when to act to the controller. Measuring devices are very useful in automation.
Let's take an example about it. Consider a process in which we are doing plastic packing by heating the packets, we designed a system in which there are two heated plates, the packet is clamped between them, to do the packaging we need to apply a measured pressure for a given time and the temperature of the plates should be maintained in working limit.
In this situation we need a pressure gauge to measure the pressure, pressure sensor to check the value of pressure and to send the real the value of pressure to the controller, thermal sensor and heater to maintain the temperature of the heated plates and a timer to make sure operation is performed in given time. All these devices will interact with controller and the process will be carried out.
Now let's look at some of the measuring instruments and the sensors used in automated system,
1. Pressure gauge-
A pressure gauge is a device used to measure the pressure of the fluid in a system, it is mounted
to the pipe for which we need the data/reading. It also helps identify if a supply line is having a leakage. Again it is very important and is used in every working system.
2. Pressure Indicator-
Pressure indicator is also used for measure the pressure in a supply line, the difference between pressure gauge and pressure indicator is, pressure indicator is digital and it measures the pressure using transducers while gauge is mechanically designed and provides analog value, the benefit of pressure indicator is, that we can provide the data to the controller easily.
3. Flow meter-
A flow meter is a device used to measure the flow of the fluid in a system, the flow in a system can be defined as volume or mass of fluid passing through a particular point on the supply pipe per unit time.
4. Flow sensor-
Again the electronic device to measure the flow is known as flow sensor.
5. Pneumatic to electric converter-
These are the devices which converts the pneumatic signal to a DC signal, which a controller can understand. The pneumatic signal causes vibration in a membrane, by using this vibration relative electrical signal is generated and that signal is sent to the controller. This processes and devices made to perform these tasks are called transducers.
A pneumatic timer is a device used in the system when a delay is required for the air when it is entering the system or is coming out of it . In above example we used a timer on the plates which decides the separation of the plates during packaging operation.