Industrial Control Panels in depth look Part 2: IO

Today we are going to be talking in depth about the different types of IO that can be wired into a panel. We will discuss how to actually wire the I/O. We will also show you some steps that are critical to ensure that the devices being wired into the panel are sending and receiving that data as intended.

Let’s first discuss the different signal types that make of the various types of IO in a panel.

Let’s first talk about Digital signals. Digital signals are designed to measure and control a value that is either on, or off. It’s easy to think of this like a common light switch in our home. We can turn it off or off, but we do not have the ability to control how much light we get, or how bright or dark the light is. This is again, how digital signals work. On or off, or True or false, or one or zero. An industrial example of this would be: the status of a motor, it is either running or not running. Or sending a command to start or stop that same motor, we only have two choices, on or off.

Now let’s talk about Analog signals. Analog signals are intended to measure and control a range of values. To better illustrate this point, think of that same light switch. Instead of just turning the light on or off, let’s assume we are using a dimmer switch. The dimmer switch gives us the ability to turn the light on and off, but also allows us to manipulate the light output anywhere in-between the fully on and fully off state of that switch. This is again, how an analog signal works. We measure and control and range of values. An industrial example of this would be: the level in a tank, or the amount of flow or pressure within a pipe.

Now that we have talked about both digital and analog signals, lets discuss how we can use those signals. In these control signals, we have the ability to either send data out, or receive data back to our panel. This data input and output is ultimately what gives that the ability to monitor and control the intended environment.

First-analog inputs

Analog signals need to be wired with a special kind of wire known as twisted shielded pair.

This kind of wire will have two conductors, as well as a shield wrapped around the wire to protect the signal from any noise or distortion.

It also has a ground wire.

This wire Must be tied to ground within the panel. Not at the instrument.

Depending on how the instrument is being powered, will determine how you will wire a analog signal. In this case the panel is providing power, which is being sent out to the instrument on this wire.

The signal that tells the PLC the value you need will come back on the signal wire, and is ultimately tied to the PLC.

Now Analog outputs
Wired much the same way,.
We don’t need to supply power in most cases
Still need to ground the TSP

Digital inputs
Power is wired to the terminal blocks and sent to the device.
Normally low voltage (24VDC)
The device will have a set of contacts, that when close will allow power to be brought back to the panel, and ultimately into the PLC.
When the PLC senses this voltage, it reads this as “true”, or “on”
Normal wire is used

Digital Outputs
Normal wire is used
Low voltage signal to a relay
Make sure the coil on the relay matches the output voltage of the PLC
The coil then switches a higher voltage output signal
Maybe to a motor or solenoid valve

By properly organizing and wiring your IO, you will be able to successfully monitor and control all devices and instruments in the field without any problems.


Additional Links -

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Manufacturers Page:
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PLCs & IO:
https://rspsupply.com/c-3872-plcs-io....
Relays & Timers:
https://rspsupply.com/c-1620-relays-t...
Sensors:
https://rspsupply.com/c-10189-sensors...
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https://rspsupply.com/c-6263-networki...
Cable Wire & Assemblies:
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