An analog input is a type of input signal that provides continuous readings from the field to the PLC. Unlike digital signals which give constant voltage readings, the analog signal can vary depending on the field conditions. The most common types of analog signals are the 4-20mA signal and 0-10Vdc signal, which can vary between 4-20mA or 0-10Vdc, depending on the field conditions.

To understand this better, let’s take an example of using a pressure transmitter to monitor the pressure of water flowing through a pipe with a range of 0-10 Bar. In this case, the transmitter outputs a signal voltage proportional to the pressure in the pipe, which can vary between 0 and 10V. This signal, being an analog input, provides a continuous reading on the pressure in the pipe.

Analog inputs help you measure variable conditions that are not indicated by discrete changes in the physical world. For example, you can use an analog input to measure the thickness of the cat on the mat by measuring the force that the cat exerts on the mat as a variable.

There are many transducers available that convert changing physical conditions into changing electrical quantities. Photocells convert the amount of light that falls on them to a changing resistance, while thermistors change their resistance in response to heat. Flex sensors, force-sensitive resistors, and many others can also be used to measure variable conditions.

## FAQs

An analog input is a type of input signal that provides continuous readings from the field to the PLC. It is not a constant voltage signal and can vary depending on the field conditions.

### What are the most common types of analog signals?

The most common types of analog signals are the 4-20mA signal and the 0-10Vdc signal, which can vary between 4-20mA or 0-10Vdc, depending on the field conditions.

### What transducers can be used to convert changing physical conditions into changing electrical quantities?

Transducers such as photocells, thermistors, flex sensors, and force-sensitive resistors can be used to convert changing physical conditions into changing electrical quantities.

## Final Thoughts

Analog inputs are essential in measuring variable conditions in the physical world. It can be used to provide a continuous reading from the field to the PLC. Understanding how it works and the types of transducers can help you choose the most suitable analog input for your application.

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