Every PLC (Programmable Logic Controller) is connected to Input / Output signals. These signals are the only way a PLC can communicate with the outside world. These Input / Output signals are connected to instruments that signal the PLC. These signals could be digital or analog depending of which type of instrument is used and what it is used for.
For example a temperature sensor would measure the temperature and send an analog value to the PLC, where a temperature switch would only send a digital value (on/off) when it detects certain temperature has been reached or not.
There are many different types of instruments; here is a list of some of them:
- Pressure and so on
We will introduce some of the many different types of instruments hoping it will give you an idea of what kind of instrument to choose based on your control system. Usually this is very closely related to the functionality of the instrument. Once the functionality of the instrument is defined then the cost of the instrument and its durability, and its environment and the options it has plays a big roll deciding the right instrument for your systems.
Not to forget the instrument you choose should be able to communication with the type of controller you are using and which type of communication you want your instruments to connect to your PLC. For example direct I/O, DeviceNet, DH+, ControlNet and so on.