Category Archives: Outputs

Wiring outputs to the plc like relays and motors.

Productivity 1000 Series PLC Contact and Coil Instructions

The Productivity Suite Software consists of more than 82 instructions divided into 13 categories for the PLC. Contacts and Coils are two of the categories of instructions. Contact instructions include NO / NC, NO Edge / NC Edge and Compare. Coil instructions include Out, Set, Reset, OR Out, Flasher, Debounce, Timed, Toggle, Program End and No Operation.

We will be looking at these instructions in the Productivity 1000 series PLC. Adding to our favorite instructions helps us to organize the instructions. We will also look at organizing your favorite instructions. Let’s get started. Continue Reading!

Wiring Interposing Relays

Interposing relay means a device that will separate two different circuits. The isolation can be for current consumption, voltage differences, voltage references or a combination of both current and voltage. We can use these relays to help connect our inputs and outputs on our programmable logic controller. (PLC) Continue Reading!

PLC Programming Example – Shift Register (Conveyor Reject)

Allot of times when programming a PLC you need to track what has previously happened. Shift registers allow you to do just that. We will look at a PLC basic tutorial of a conveyor belt and reject station. Following the 5 steps to program development this PLC programming example should fully explain the function of shift registers. Ladder will be our PLC programming language.

We will be using the Do-more Designer software which comes with a simulator. This fully functional program is offered free of charge at automation direct.

Define the task:

What has to happen?
Conveyor Reject 0

A start pushbutton (NO) is used to start the conveyor and a stop pushbutton (NC) is used to stop. Sensor B detects product on the conveyor belt and sensor A will detect if it is too large and needs to be rejected. The product is tracked along the conveyor belt and when under the reject station the Reject Blow Off will expel the bad product. Product is randomly placed on the conveyor belt, so an incremental encoder is used to track the conveyor movement. The reset pushbutton (NO) will signal that all of the product on the conveyor has been removed between the sensors and reject blow off.

Define the Inputs and Outputs:

Inputs: Start Switch – On/Off (Normally Open) – NO Stop Switch – On/Off (Normally Closed) – NC Reset Switch – On/Off – NO Motor Encoder – On/Off – This will give a discrete signal when the conveyor is moving. It picks up the movement of the free wheel. Sensor A (Part Reject) – On/Off – NO Sensor B (Part Present) – On/Off – NO

Outputs: Motor – On/Off (Conveyor Run) Air Blow Off – On/Off (Reject)
Inputs_Outputs

Develop a logical sequence of operation:

Fully understanding the logic before starting to program can save you time and frustration.

Sequence Table: The following is a sequence table for our conveyor reject application.
Sequence Table

It is a simple sequence table, but clarifies the following: When power goes off and comes on the sequence will continue. This means that the shift sequencer must be memory retentive. Sensor A and B must be on to get tracked with a shift register.

Shift Registers: The Shift Register (SR) instruction shifts data through a predefined number of BIT locations. These BIT locations can be a range of BITs, a single Word or DWord, or a range of Words or DWords. The instruction has three inputs. Data, Clock and Reset. The data input will load the beginning bit with a ‘1’ if it is on or ‘0’ if it is not. Clock input is used to shift the data through the shift register. In our example, we will be using the encoder on the conveyor to track the reject container. So each pulse of the clock represents a distance on the conveyor. The last input is the reset. It will place ‘0’ in all of the bits within the shift register.
Shift Register

Develop the PLC program:

Start and stop of the conveyor motor.
Program Conveyor Reject 1

Shift register to track the rejected parts. This will move the bits with each pulse of the encoder. Note that the ‘V’ memory is used because it is memory retentive.
Program Conveyor Reject 2

This will look at the bit in front of the reject station. We can measure and count off the length (conveyor) and then find out what the bit location will be at the reject location.Program Conveyor Reject 3

Test the program:

Test the program with a simulator or actual machine. Make modifications as necessary. Remember to follow up after a time frame to see if any problems arise that need to be addressed with the program.

Conveyor Reject

Notes: Sometimes you can use multiple shift registers in your program. This can be helpful if you want to actually track the container as well as the rejects. You could also use bit shift right (BSR) and bit shift left instructions (BSR) to do the same thing as we did with the shift register instruction. In the Do-more PLC it is rotate left (ROTL) and rotate right (ROTR) instructions. Always check your instruction set of the controller that you are working with before starting to program.

Watch on YouTube : PLC Programming Example – Shift Register (Conveyor Reject)

Additional information on shift registers can be seen at the following URL:
https://accautomation.ca/plc-programming-example-sorting-station-shift-register/
This PLC programming example will look at sorting coloured tags into three different exits. The 3D simulation will use three different shift registers to trigger when to direct the correct colour tag.
Watch the sequence of operation video below.
Watch on YouTube : PLC Programming Example – Sorting Station Testing

If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.




How PLC Outputs Work

This post is a further follow up from my original ‘Here’s a Quick Way to Understand PLC Inputs and Outputs’. There are basically two different kinds of PLC outputs, Discrete and analog. Discrete outputs are either ‘ON’ or ‘OFF’; 1 or 0. You can think of them as a single light bulb. Analog outputs have a range to them. They are outputs that usually will control proportional valves, drive speeds, etc. They usually have one of the following signals that are outputted from the PLC: 4-20mA, 0-10VDC, 1-5VDC.

Discrete Outputs
PLC Outputs

The above diagram has three outputs. A coil, light and motor. The Ladder outputs Y0, Y1 and Y2 control the outputs respectfully. You will notice that when the Ladder output turns on, the corresponding output card bit LED turns on. This then will energise the output hardwired to the device.

The outputs are turned on or off at the end of every PLC Scan. The PLC logic is solved left to right, top to bottom in most PLCs. Physical outputs are not set / reset until an I/O refresh is performed at the end of every scan. This means that if I have a scan of 1msec, then the maximum time it will take to turn on/off the output is 1msec.

PLCs will sometimes have the ability to update the I/O in the middle of a scan. Please refer to your PLC manufacturers manual for this instruction. This can be used for updating the I/O quickly or controlling stepper drives for motors by giving them a pulse train output from the discrete PLC output. A pulse train is just a quick series of on/off states of the output.

Analog Outputs
PLC Analog Output to Motor Speed

An analog output converts a digital value to a voltage or current level that can be used to control (vary) physical outputs. In the example above we are controlling the speed of the motor. Words in the PLC will control the analog value.
Example:
4 – 20 mA current Output – 8 bit resolution
4 mA = 00000000 base 2 = 00 base 16
20 mA = 11111111 base 2 = FF base 16
For a review of numbering systems, follow the link below:
What Everybody Ought to Know About PLC (Programmable Logic Controller) Numbering Systems

In the industrial environment noise from variable frequency drives, improper grounding, etc. can interfere with your analog input. The following post will show a quick method to reduce this noise.
The Secret Of Getting Rid Of Noise On Your Analog Signal

Previous Post:
How PLC Inputs Work

Watch on YouTube : How PLC Outputs Work

If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.




The Secret Of Getting Rid Of Noise On Your Analog Signal

Allot of times in industrial environments we get noise on the analog signal input to PLC’s or other controllers. The noise can be generated by motors, bad wiring, etc.

Placing a 1- 100 uF capacitor on the input signal and ground (common to the cabinet)  will reduce the noise that the input is receiving.

If you have any questions or need further information please contact me.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.




Here’s a Quick Way to Understand PLC Inputs and Outputs

The term I/O means Input/Output. I/O can come in two different types; Discrete or Analog Most people starting out leaning about programmable logic controls (PLC) are taught all about discrete input and outputs. Data is received from devices such as push-buttons, limit-switches etc. and devices are turned on such as motor contactor, lights, etc. Discrete input and output bits are either on or off. (1 or 0) The following program will show a motor control circuit stop start. Motor off:

Motor on:

Analog inputs Common input variables for analog are temperature, flow, pressure, etc. They are converted to an electrical signal into a PLC analog input. Standard electrical signals are 0 – 20 mA, 4 – 20 mA, 0 – 10 volts DC, -10 – 10 volts DC. Note: It is recommended that a 4 – 20 mA signal is best. If voltage is required, a resistor can be added to get a voltage input. Analog outputs Common output variables for analog are speed, flow, pressure, etc. They are converted from a word in the PLC to the output of the analog. The range of signal is then outputted to the device to control the position, rate, etc. Standard electrical signals to the device are 4 – 20 mA, 0 – 10 volts DC, -10 – 10 volts DC. Both Analog Inputs and Outputs use words to determine the signal going to or from the device. Example: 4 – 20 mA current Input – 8 bit resolution 4 mA = 000000002 = 0016 20 mA = 11111111= FF16 Example: 4 – 20 mA current Output – 8 bit resolution 0016 = 000000002 = 4 mA FF16 = 111111112 =20 mA For a review of numbering systems, follow the link below: What everyone should know about PLC numbering systems

 

Let me know if you have any questions or need further information.
Thank you,
Garry



If you’re like most of my readers, you’re committed to learning about technology. Numbering systems used in PLC’s are not difficult to learn and understand. We will walk through the numbering systems used in PLCs. This includes Bits, Decimal, Hexadecimal, ASCII and Floating Point.

To get this free article, subscribe to my free email newsletter.


Use the information to inform other people how numbering systems work. Sign up now.

The ‘Robust Data Logging for Free’ eBook is also available as a free download. The link is included when you subscribe to ACC Automation.