Categories
PLC

Control Panel Fan Location

Introduction

In designing Industrial Control panel, the air must enter on the lower part of the control pane; and it must exit at the upper part of the control panel

Reasons

  • Hot air is lighter than the cold air it means that the hot air inside the control panel is easier to exhaust if you will put a fan at the upper part of the control panel.
  • It is easier to make the cold air to enter the control panel if you will put a fan at the lower part of the control panel.

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Categories
Electronics PLC

Relay VS Transistor (Output Voltage)

Introduction

   If you are going to buy a PLC, types of output is one of the thing that you need to consider, I hope this article can help you to choose what kind of PLC output you need. There are two types of PLC output, the relay output and the transistor output. Watch: Types Of PLC Descrete Output (Relay and Transistor)

Relay VS Transistor (Polarity)

Relay output = Output Polarity can be Positive or negative depending on the wiring Configuration. Watch: PLC wiring configuration

Transistor output = Output polarity is fixed (sinking for negative output, sourcing for positive output).

Relay VS Transistor (Response)

Relay output = Relay output performs mechanical switching which response is the same as the response of traditional relay.


Transistor output = Transistor output performs electronic switching which is a lot faster than mechanical switching.


Note: For some applications like servo motor pulse control, transistor output is much better choice that relay output, because sometimes servo motor controller requires 100,000 pulse per seconds to control the servo motor and relay output is not capable of performing this requirement.

Relay VS Transistor (Output Voltage)

Relay output = Some of the relay output can be use to produce AC voltage (Check the PLC specifications).


Transistor output = Transistor output can only used to produce 24 Volts DC.

Relay VS Transistor (Stored Energy)

Relay output = Relay output is not affected by stored energy from inductive load.


Transistor output = Transistor output can be damage by stored energy from inductive load.


Note: In case that you need to use PLC transistor Output together with inductive load you can connect diode in parallel with the inductive load in reverse bias to protect the PLC transistor output from stored energy.



watch: Use Diode for Protection Reverse polarity protection and Stored Energy Protection

 

 

 

 

Categories
Electronics PLC

PLC output Protection

Introduction

“Prevention is Better than cure”
In automation industry there are some reasons why our equipment get damage or malfunction, but if we know these reasons we can come up with the solution to prevent the damage that may occur, engineers are one of the intelligent people here in the world, they can fix the damage but if we can put some protective equipment and preventive method, We can reduce the production downtime.

Causes of PLC Output Damage

  • Wrong wire termination
  • Over Current
  • Stored Energy

Wrong Termination

Cause

  • Human Error
  • Wrong Circuit Diagram

Solutions

  • Supervisor / Engineer must check and approved the diagram before project execution
  • Loop checking
  • Yellow Tagging

Over Current

Cause

  • Defective Equipment / Field devices
  • Short Circuit

Solutions

  • Preventive Maintenance
  • Install fuse for short circuit protection

Stored Energy

Cause

  • Inductive Loads

Solutions

  • Install Diode (reverse bias) in parallel with the load

Related Article


Reference Video

 

 

 

 

Categories
Electronics PLC Protection

Protect your Instrument from stored energy cause by inductive load

Introduction

In some cases in automation industry sometimes the instruments get damage because of direct mechanical contact like limit switch, but we know the reason behind this,  limits switches and other instrument that makes mechanical contact with actuators like pneumatic cylinders and it get damage because it receives force repeatedly that might  cause broken sensor mounting and broken spring, but some instruments might also receive damage from stored energy cause by inductive load.

What is inductive load?

Inductive loads are electrical instruments that compose of coils that generates magnetic field such as:

  • Relay
  • Magnetic Contactor
  • Motors
  • Incandescent lamp 

How does inductive load causes damage to instruments like PLC?

 The stored energy cause by inductive load will try to pull current at port Y0 even if Y0 is not energize anymore (refer to the picture below). let’s say that Y0 will turn “ON” for 1 second then it will turn “OFF” for 1 second, the stored energy at the relay will try to pull the current at Y0 every time that the relay turns “OFF”.

How to Protect the instrument like PLC from Stored energy cause by inductive load?

The only way to protect the PLC from stored energy is by consuming it, you must have a component that will absorb the energy so that it will not cause damage to the other instruments. You can terminate a diode in parallel with the inductive load to absorb the stored energy.(refer to the picture below)

Caution: 

  • Diode must be connected in reverse bias, if diode is connected in forward bias the load will be shorted and that will cause damage to your instrument as well.
  • To get the proper diode, the maximum current and voltage must be consider.

Note: 

  • You can replace the Incandescent lamp to LED lamp if you don’t like to terminate a diode. (LED lamp is not an inductive load, but it can be use as an indicator like incandescent lamp)

Reference Video: