Feb 19, 2018

Auto Mains Failure PLC Program using Omron PLC

"Auto Mains Failure System" is Employed for Auto startup of the DG when the mains supply fails. This is a very common system and is the first step in DG synchronization. Here we will see that what is the basic concept in AMF? What hardware is required to set up AMF and how PLC Programming is done.


Auto Mains Failure PLC Program


First of all let us understand what is AMF?

Generally, all the major industries/companies/institution have the DG for power backup, but when main power is cut off, someone has to go to start the DG and this takes time and also a man has to be kept for this purpose. So to eliminate this process PLC panel is installed to Auto start the DG when main power fails. Subscribe to Automation-Talk by Email for more such tutorial.


Working of Auto Mains Failure


When the main power goes, a signal is received to PLC and after 2 minutes DG starts. When the main supply fails signal is received by PLC then after a delay time (can be from 1 to 2 minute), the output for ACB/Contactor of DG is ON and DG starts automatically. Also, the ACB/Contractor of the main transformer if sent OFF command.

When main power comes then the signal is again sent to PLC and PLC off the ACB/Contactor of DG and after 2 seconds it on the ACB/Contactor of the main transformer and after 30 seconds it off the DG. DG is sent OFF command a little late so that the load born by DG for a long time can be compensated by running at no load for some time.

NOTE:- In 'No' condition, the ACB/Contactor of both DG and Main transformer should be ON.

So this is the main concept in DG AMF system.


In a simple system, there are generally 4 inputs and 4 outputs.

Inputs:-

1. DG ACB/Contactor close feedback.
2. Transformer ACB/Contactor close feedback.
3. Transformer Voltage Available.
4. DG Voltage Available.

Outputs:-

1. DG start.
2. DG Stop
3. DG ACB/Contactor close.
4. Transformer ACB/Contactor close.

For your better understanding below is the sample program. If you have any doubts then just write in comments and we will get back to you. Download the PLC Program for AMF:- Click here to Download.

Hope you like this article, if you do comment below and share it on social media. Hope to see you on next article.

Jan 21, 2018

Mnemonic Names of Commonly used Instructions in PLC

Mnemonic Names of Commonly used Instructions in PLC


In our daily programming of PLC like ABB, Allen Bradley, Omron, etc. we use Mnemonic and some of the very commonly used instructions in PLC are as follows. We know we have missed many of them, so please help us to complete the list by commenting the other mnemonic in the comment section.



Mnemonic Names of Commonly used Instructions in PLC


INSTRUCTION -------------------------------- MNEMONIC NAME

1. Examine if closed --> XIC --| |--

2. Examine If Open --> XIO --|\|--

3. Output Energized --> OTE --(OTE)- -

4. Branch Start --> BST

5. Next Branch --> NXB

6. Output Latch --> OTL --(L)--

7. Output Unlatch --> OUT --(U)--

8. One shot Rising --> OSR

9. Timer On-Delay --> Ton

10. Timer off-Delay --> Toff

11. Retentive Timer --> RTO

12. Count Up --> CTU

13. Count Down --> CTD

14. Reset --> RST --(RST)--



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Dec 27, 2017

Importance of Emergency Button in Control Panel

Designing any electrical machine or its control panel involves proper planning, designing and commissioning. All these steps are very important for effective working of the machine and operation through it. Machine Planning is very important in the designing of the machine as it decides the future of production through it. In the planning process of Electrical machine control panel, it involves many important aspects to be followed. Subscribe to Automation-Talk by Email.


Emergency in PLC programming


Emergency or Stop button plays a very important role in every control panel and every engineer should include Emergency button in there panel which should be in reach of the machine operator. While making a PLC program, emergency input should be used correctly so that it stops the whole machine at the time of need.


PLC Programming of Emergency Button

Programming an emergency button is very easy as you just need to add a normally closed contact in series with your PLC program. This you can do by adding the emergency contact on every rung of our ladder program at the start or can just actuate a memory bit with that and can use that memory bit everywhere you want to stop the program.

There is a big difference between emergency and a stop button though they look alike. So don’t do the mistake of not using an Emergency button in your panel.


Using Emergency button in Relay logic

If you are using only relay logic for your control panel, then also you can include an emergency button in the panel just add emergency button (NC contact) in series at the start of your electrical circuit.


Dec 17, 2017

Different Types of Motor Load Meaning

While selecting the AC motor for an application, we always first lookout that what type of load will be driven by AC Motor i.e. constant Torque load or variable torque load. Almost all of the automation and plc engineers must have seen all such type of loads. Also while selecting the VFD for an AC motor we have to select the VFD according to the Load type. But do we actually know what this load type means?

Well if not, then in this post we will try to understand the different types of load.


Different Types of Motor Load Meaning


What is Constant HorsePower Load?

The constant horsepower load is that type of load in which the torque requirement is more at low speed and as the speed increases the torque requirement decreases. This type of load examples can be found drill machines, lathe machines, and metal removing applications.



What is a Constant Load Torque?

In constant torque load, the torque requirement is always the same irrespective of the load speed. If we take the example of conveyor then the torque requirement of a conveyor is always same whether it is running at low speed or high speed.


What is Variable Type Load?

Variable torque load is a term which is used for loads that require low torque at low speeds and high torque at high speeds.

Examples of Variable type load are centrifugal pumps and fan. In the market, there are special VFD available for such type of applications that saves a lot of energy.


Hope that after reading this article, we now understood the different type of load meaning and next time we can easily identify the type of load that a motor is driving. Don't forget to subscribe to get all latest updates and also like our facebook page if you like Automation Talk.

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Nov 24, 2017

Difference Between Reflective, Retro Reflective & Through beam Optical Sensor

Sensors are the very important part of automation industry and are categorized into many types, like proximity sensor, level sensor, pressure sensor, photosensor or optical sensor etc. We widely used these sensor in our industry for object detection, fault detection etc. Sensor are those sensing device which senses and convert that to the electrical signal. In this tutorial we will learn what is the basic difference between a reflective or diffused photo sensor, retro reflective & through beam Optical or photo sensor. Subscribe to Automation-Talk by Email.

Difference Between Reflective, Retro Reflective & Through beam Optical Sensor
Image source: fargocontrols.com

On seeing the above picture, you must have got an idea that what is the difference between these 3 types of optical sensor.

Through beam optical sensor has transmitter and receiver as a separate device and work on the principle that whenever a object comes between transmitter and receiver a signal is sent. Used when sensing distance is large.

Retro reflective type of optical sensor has transmitter and receiver on same housing and they require a reflective surface called reflector for there working.

Reflective optical sensor are also called diffused photo sensor and has transmitter and receiver on same housing but they do not require any reflector for there working. Object to detected itself work as a reflector.

The main advantage of optical sensor's is that they do not do the difference between the object, unlike proximity sensor.

Nov 7, 2017

Motor Related Common Electrical Terms - Part 2

In the last section we studied about some of the frequently used motor electrical parameters in our day to day work. We have already understood about the different types of AMPS rating that a motor nameplate have, in this post we will try to understand about the design of motor that is what type of torque and speed curve motor have, we will also look in to efficiency, frame size, and frequency. Subscribe to Automation-Talk by Email.


Motor Related Common Electrical Terms

What Does Design of AC Motor Indicates


There are generally four types of design A B C D that an AC Motor can have. The design of AC Motor just indicates the type of speed v/s torque curve that the motor will have. The speed v/s torque curve for all the designs of the motor is below.



The standard industrial motor will mostly have the design B, it has reasonable starting torque with average speed and starting current with a good performance. In the above curve, we see that design C has the high starting torque so this type of motor is used where we have to start the high loads. Design D is the so-called high slip motor which tends to have very high starting torque but has high slip RPM at full load torque. Design D motors are generally suited for press and elevator applications. Design A motors are not particularly specified but are used where the high pull out torque is required.


What does efficiency of AC Motor Means?


Efficiency is indicated on the nameplate of the motor and in simple terms, it means that it is the amount of input energy that is converted into work. We should always select a motor that has high efficiency.


Meaning of Frame Size in AC Motor

As everything in this world has some size, same is the case with the motors. As the motor HP increases or RPM decreased the frame size of the motor increases. NEMA (National Electrical Manufacturers Association) has prescribed standard shaft diameter for the particular frame size so as to maintain a standard among all the motor manufacturers in the world.


What does Motor Frequency Indicates


Frequency on the motor nameplate means that for which input frequency motor is designed to operate. Most common motors have operating frequency of either 50 or 60 Hz.

We have understood some of the more common electrical terms in this post. We will also cover other commonly used electrical motor parameters in the upcoming post. If u have any doubts at any point please feel free to write in the comment section.

Oct 30, 2017

How To Reduce Electromagnetic Interference in Servo Drives

Motion Controllers and Servo drives are used in machines for the better controlling and accurate positioning purpose. The one thing which we should keep in mind while installing the motion control panel is to have a safe and healthy environment for the Servo Drive and Motor operation i.e the environment should be free from any Electromagnetic Interference (EMI). EMI can dramatically reduce the performance of the system and can lead to various other problems. In this post, we will see that what practices should be followed in order to have the minimum or zero effect of EMI.


Reducing EMI effect by following Standard Wiring Practices



How To Reduce Electromagnetic Interference in Servo Drives


Generally, all major servo drive and motor manufacturers have their products following CE compliance. But using CE approved components will not guarantee a CE compliant System. The whole depends upon the components In drive, interconnection procedure, and installation method. So we should follow the practices by which the EMI effect can be minimized.

Electromagnetic Interference is generally generated by High frequency switching circuit. EMI generated inside the enclosure is either conducted or radiated back inside the enclosure only, so proper measures should be taken in order to avoid EMI conducted back into the main power source. Below picture illustrates that how EMI is conducted or Radiated back to the main power source.


EMI Radiation Conduction


Steps to Follow for Reducing/Minimizing Conducted EMI Effect



In order to reduce the Conducted High-Frequency noise, an EMI filter should be installed in series with the power supply. This EMI filter should block frequencies causing Interference and also not saturates at the current level required for normal operation. The EMI filter should be installed in such a way that it blocks EMI conduction to main power supply.

Shielded and Screened cables should be used wherever appropriate. Power Supply cables should be kept separate from Signal Cables and all cables should be as short as possible. Ground wires should have sufficient cross-section area in order to minimize the Skin Effect and conduct EMI to ground. Connect the EMI filter properly as shown below.

EMI Filter Correct Wiring


How to Remove the Radiated EMI Interference:-

Several points should be kept in mind to reduce the radiation of EMI back to the main power source. If there are any holes in the enclosure than the Holes should be as small as possible. Use conducting Gasket at seams of the door. Avoid grounding the Screens/Shield at only one end, doing this can dramatically increase the radiated EMI. If you found any particular cable is creating much EMI than it can be reduced by ferrite beads.


We will summarize the important points below:-

All cables that connect to motor control should be shielded. Input power cable and Motor Output cable should be separate and positioned independently. Grounding must be done properly and all cables should be laid close to the ground plane. The motor cable shield should be connected to a motor ground terminal at motor side.

Motor Correct Wiring Procedure

The above picture shows the standard wiring procedure for better efficiency.

The shield/screen of all cables connected to the control must be grounded to the control by connecting the shield to the control’s “Ground” terminal. The cables include the motor cable, input cables, feedback cables regen/dynamic resistor cables and other control cables.Subscribe to Automation-Talk by Email.

If you strictly follow all the steps told above, then definitely the EMI effect will be minimized and will achieve better efficiency and increased life of your product. In upcoming articles, we will further discuss the more advanced things to eliminate the EMI effect completely from your system. Till then you can subscribe to Automation-Talk by Email to get all latest updates by eMail.

Oct 9, 2017

PID Control with Auto Tuning in Omron PLC

PID control as we all know is a fundamental thing used in process automation. For PID control we generally use PID Controller, but in Omron PLC there is one exclusive instruction for PID purpose. This instruction is very helpful in many application where we can minimize cost by using software PID inside PLC. In this post, we will see that how to use this PID Instruction in Omron PLC.

PID Control Feature In Omron PLC


Omron PLA is very popular in the Automation industry and used in a wide range of applications. Omron PLC have exclusive feature that we can create a PID inside PLC by using an PLC Instruction. The name of PLC instruction is PIDAT.

Syntax:- PIDAT S C D

Where S is the Input word, C is the control/Parameter Word and D is the first output word.


When the input condition of this instruction is on then it performs the PID control on the bit in word S according to the control word C. The different bits of Control word C defines the PID process parameters. Let us see the meaning of each bit of control word C. The word C defines the target value of the process being controlled.

C+1 defines the proportional band i.e the parameter for P action expressing the pro­portional control range/total control range. C + 2 defines Tik Integral Constant, a constant expressing the strength of the integral action. As this value increases, the integral strength decreases. C+3 stands for Tdk Derivative Constant, constant expressing the strength of the deriva­tive action. As this value increases, the derivative strength decreases. C+4 stands for the sampling period, the sampling period can be designated in units of 10 ms (0.01 to 99.99 s), but the actual PID action is determined by a combination of the sampling period and the time of PID instruction execution (with each cycle).

Below is the diagram explaining PID action.

PID Control with Auto Tuning In Omron PLC

PID action combines proportional action (P), integral action (I), and derivative action (D). It produces superior control results even for control objects with dead time. It employs proportional action to provide smooth control without hunting, integral action to automatically correct any offset, and derivative action to speed up the response to disturbances.

This instruction is very useful for PID block creation. Dont forget to subscribe to get all latest updates. Subscribe to Automation-Talk by Email.

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