Category Archives: Inputs

Wiring inputs to the plc like switches and proximity sensors. This also includes analog input signals.

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!

Create an Analog Voltage Input Tester for a PLC

We will create a simple and inexpensive analog voltage tester for a PLC using a potentiometer and a 9VDC battery. The potentiometer will be 5K ohms. This should be enough impedance for most analog inputs of the programmable logic controller. (PLC) Voltage impedance for analog voltage inputs are in the mega ohm range where current input is typically 250 ohms. Our tester will be for analog voltage inputs (0-10 VDC). Check your input specifications before wiring anything to your PLC. I have used this tester for other voltage inputs along with a meter to ensure that the voltage levels do not get out of range for the input signal.
Analog inputs to the PLC are continuous and can come in a variety of signals. These signals can come from temperature, flow rate, pressure, distance, etc. 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!

How PLC Inputs 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 inputs, Discrete and analog. Discrete inputs are either ‘ON’ or ‘OFF’; 1 or 0. You can think of them as a single switch. Analog inputs have a range to them. They are inputs that usually will sense pressure, temperature, height, weight, etc.  They usually have one of the following signals that are inputted into the PLC: 4-20mA, 0-10VDC, 1-5VDC.

Discrete Inputs
PLC Input

The above diagram has two inputs. A normally open (NO)  and a normally closed (NC). When we talk about normally open and close, think of the condition of the input if no one touches anything. A normally open contact will not turn on the input to the PLC card in its ‘normal’ state. The normally closed contact will turn on the input to the PLC card in its ‘normal’ state.

Normally Open Input
The NO contact when activated will complete a circuit and turn on the PLC input. Ladder logic will then turn on if you use a normally open (Examine On) input in your program. See above diagram.

Normally Closed Input
The NC contact when activated will break a circuit and turn off the PLC input. Ladder logic will then turn off if you use a normally open (Examine On) input in your program. See above diagram.

As you can see with the diagram above this can get tricky to determine the on/off condition of the input. PLC logic can convert any signal by using normally closed (Examine Off) inputs in the program. In the field, I usually look at the PLC input lights, and wiring diagrams to determine the current state of the input. This is before diving into the program to troubleshoot.

Here is a link to wiring up discrete 3-wire sensors in the field. Here’s a Quick Way to Wire NPN and PNP devices

Analog Inputs
BinMaster Analog Input

An analog input converts a voltage or current level into a digital value that can be stored and processed in the PLC. They use words to determine the signal coming from the device.
Example:
4 – 20 mA current Input – 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

Here are some additional posts that you might find helpful.
How to make a Start / Stop / Jog circuit in a PLC
The Secret of Using Timers
The Secret of Using Counters

Watch on YouTube : How PLC Inputs Work

Watch on YouTube : Wiring (Testing) Analog PLC Input Click

Watch on YouTube : Wiring (Testing) Analog PLC Input Omron CP1H

Watch on YouTube : Wiring Contact (Discrete) PLC Inputs

Watch on YouTube : Wiring PNP Sensor to PLC

Watch on YouTube : Wiring NPN Sensor to PLC

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 Wire NPN and PNP devices

Here’s a Quick Way to Wire NPN and PNP devices

I get asked often on how to wire NPN and PNP devices to the programmable logic controller. This can be confusing at first when looking at the wiring diagrams. I have managed to destroy a few sensors in the process….. so lets get started and I will share my experiences.

E2A_7069B_7l E2A_7002A_7l
NPN and PNP refer to the transistor in the output device.
NPN – Negative Positive Negative Switching. Sometimes referred to as ‘Sinking’ the load.  People have told me that when the NPN sensor blows it has a tendency to blow in an open state. (No Signal)
PNP – Positive Negative Positive Switching. Sometimes referred to as ‘Sourcing’ the load. People have told me that when the PNP sensor blows it has a tendency to blow in a closed state. (Signal On)

When the sensor blows, (malfunctions) it usually will also take out the power supply. (Fuse) It generally does not matter if you use NPN or PNP sensors provided they are all connected to the PLC using isolated commons.

You cannot mix PNP and NPN sensors on the same common point for inputs to the PLC. If you do mix the sensors, then the different common points on the PLC must be isolated from each other. This means that the commons are not connected internally to each other. Not ensuring this takes place will provide a short across the power supply and blow your sensors and supply. In general, machines tend to use all NPN or all PNP only.

Colour coding of the wires vary. Do not always rely on the colour code of the wires for connection. Refer to the wire diagrams in the documentation.

The following is a wire diagram of an open collector PNP sensor. You will notice that the load appears between the 0V (Blue)  and Switching wire (Black). When connecting to the PLC, the PLC input acts as the load. The 0V (Blue) will be attached to the common input and the Switching wire (Black) will be attached to the input number.PNP1

The following is a wire diagram of an open collector NPN sensor. You will notice that the load appears between the +V (Brown)  and Switching wire (Black). When connecting to the PLC, the PLC input acts as the load. The +V (Brown) will be attached to the common input and the Switching wire (Black) will be attached to the input number.NPN1

As you can see a direct short will be created if NPN and PNP sensors are wired into the PLC on the same common. The following shows an example of wiring of the 3 wire sensors into a PLC with isolated commons.

NPN_PNP_PLC

Watch on YouTube : Wiring NPN Sensor to PLC

Watch on YouTube : Wiring PNP Sensor to PLC

Watch on YouTube : Wiring Contact (Discrete) PLC Inputs

Wiring Interposing Relays
Watch on YouTube
: Wiring NPN and PNP Sensors into the PLC with an Interposing Relay
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 is a Method That can Help You with Difficult Level Sensing

Turn a capacitive proximity sensor into a level sensor. This is ideal for tanks and vessels that you cannot drill through the side for mounting.

Wrap bare wire around the sensing head and extend it to the length you need to detect. Insulate the wire using electrical tape all the way down, but leave the end exposed. This acts like an antenna. Anything touching the end will now be detected. I have used 14 and 12 awg wire, depending on the application.

This is ideal for hard to mount areas. You can bend the wire any way you want as long as the insulation (electrical tape) is not exposed.I have had the wire extend up to 30 feet from the sensor without an issue.

Some quick information about capacitive proximity sensors.
A capacitor is defined as two electrically charged plates separated by a dielectric. In the case of a capacitive proximity sensor, the dielectric is the material that you are trying to detect. As the material moves closer to the electrostatic field of the sensor, oscillation begins. It will get past a threshold and trigger the output to switch.

Some common dielectric constants for material:
Glass – 5
Wood – 2.7
Paper – 2.3
Air, Vacuum – 1
Water – 80
Once you know the dielectric constant you can determine the sensing range (Sr) by a chart that usually comes with the sensor or in the manufactures manual.

Example: Water is 80 so the sensing range is 100%

I generally just try the sensor to determine if it will be suitable for the application.

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.




Get Rid Of Surges That Are Destroying Your PLC Outputs

DC Solenoids are the worse culprits for electrical surges on your system. When the electrically generated field collapses an opposite polarity voltage is generated. This voltage spike can be high enough to weld the contacts on a PLC output relay.

To protect your PLC output relay, use a diode to ensure that when the solenoid switches off the voltage spike is released through the diode instead of the relay.

 

The diode should be rated to handle 10 times the voltage that you are switching and enough for the current flow of the circuit.

Parts of the diode:

The cathode of the diode is marked by a band.  The electron flow will only occur in one direction.

Installation:
Install the diode as close as possible in parallel with the solenoid. The cathode should be wired to the positive source of the solenoid. (Dissipate negative polarity voltage spike)

Note: You could also install an interposing device to handle the surge such as a SSR. (Solid State Relay) This is generally more money, space in the panel and wiring.

Note: Allot of solenoids come already with surge suppressing diodes from the manufacturer. If not, you will usually need this information when troubleshooting and discover your welded contacts of the output relay.

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.