Basic NOT gate operation explanation using electrical wiring diagram and PLC ladder diagram

Application:-Explain the NOT gate operation using electrical diagram and ladder diagram language. Draw electrical diagram for electrical panel in which lamp should be on when switch is off and lamp should be off when switch is off. Also write PLC program for this application using ladder diagram language.

Components:-Programmable logic controller, Electrical panel, wires, 24V DC switches with NO contacts, 24V DC indication lamp, 24 VDC relay,24V DC source.

Diagram:-Electrical wiring diagram and truth table of NOT gate operation

Explanation:-

In this application we need to use NOT gate logic. As shown in figure we can draw electrical diagram for NOT gate operation so that we have taken NO contact of switch S1 to operate lamps as per the NOT gate logic. Hence when switch is ON, relay is operated and lamp will be OFF due to NC contact of relay and when switch is OFF, lamp will be ON.

We can easily understand the NOT gate function with truth table,

If S1=ON, then R=0

If S1=OFF, then R=1

So NOT gate inverse the logic.

PLC program:-

Write the ladder program for NOT gate operation using ladder diagram language. Here for ladder logic we can use any PLC system. For PLC logic we need digital inputs and outputs.

For our application all switches are digital inputs and lamp is digital output. So define digital input address and output address as per below explanation,

Digital inputs:-

S1=I0.0

Digital Output:-

Lamp=Q0.0

Memory coil:-

Memory bit-M0.0

PLC program Explanation:-

In network 1 we have used NO contact of switch S1 (I0.0) to operate memory bit (M0.0).So when S1 (I0.0) is ON memory coil (M0.0) is ON and switch S1 (I0.0) is OFF, memory coil (M0.0) will be OFF.

In network 2 we have used NOT gate function so when switch S1 (I0.0) is ON, it will inverse logic and makes lamp (Q0.0) OFF. And when S1 (I0.0) is OFF, lamp (Q0.0) is ON

Basic OR gate operation explanation using electrical wiring diagram and PLC ladder diagram

Application:-In electrical panel there are two switches given for panel ON lamp. Both the switches are optional, the lamp can be ON either by switch 1 or switch 2.Draw truth table, electrical wiring diagram and write PLC program for this application.

Components:-Programmable logic controller, Electrical panel, wires, 24vDC switches with NO contacts, 24VDC indication lamp, 24 VDC relay.

Diagram:-Electrical wiring diagram and truth table of OR operation

Explanation:-

As per our application, we can use above application for OR gate explanation. In application we are using two switches and one lamp for indication. If switch 1 or switch 2 pressed, indication lamp should be ON. So in above electrical wiring diagram we have used S1 and S2 in parallel connection so electrical supply can flow either from S1 or S2.

In truth table we can easily understand the conditions of OR gate,

As per truth table,

If S1=ON OR S2=ON, then R=1

If S1=ON OR S2=OFF, then R=1

If S1=OFF OR S2=ON, then R=1

If S1=OFF OR S2=OFF, then R=0

So the output will be OFF only in the last condition.

PLC program:-

Write the ladder program for OR gate operation using ladder diagram language. Here for ladder logic we can use any PLC system. For PLC logic we need digital inputs and outputs.

For our application all switches are digital inputs and lamp is digital output. So define digital input address and output address as per below explanation,

Digital inputs:-

S1=I0.0

S2=I0.1

Digital Output:-

Lamp=Q0.0

Memory coil:-

Memory bit-M0.0

PLC program Explanation:-

In network 1 we have considered two digital inputs for two switches S1 and S2. So we have taken NO contact of S1 (I0.0) in parallel with S2 (I0.1) for OR operation. So when S1 or S2 ON, memory bit (M0.0) will be ON.

In network 2 we have taken NO contact of memory bit (M0.0) to operate panel ON lamp (Q0.0).

Basic AND gate operation explanation using electrical wiring diagram and PLC ladder diagram

Application:-Set wiring in the electrical panel so when operator has to operate two switches to operate one lamp. Make electrical control wiring using two switches and one lamp. Also draw truth table for application and write PLC program using ladder diagram language.

Diagram:-Electrical wiring diagram and truth table of AND operation

Explanation:-AND gate operations very important logic in various industrial application. For example purpose we have taken two switches S1 and S2 as shown in above figure. So if operator wants to ON lamp, he has to ON both the switches as per the AND operation. So S1 and S2 must be ON if we want to ON lamp.

In truth table all the conditions has been shown for explanation, it can be easily learned by simple conditional logic,

As per truth table,

If S1=ON AND S2=ON, then R=1

If S1=ON AND S2=OFF, then R=0

If S1=OFF AND S2=ON, then R=0

If S1=OFF AND S2=OFF, then R=0

So output will be ON only in first condition.

PLC program:-Write the ladder program for AND gate operation using ladder diagram language

Here for ladder logic we can use any PLC system. For PLC logic we need digital inputs and outputs.

For our application all switches are digital inputs and lamp is digital output. So define digital input address and output address as per below explanation,

Digital inputs:-

S1=I0.0

S2=I0.1

Digital Output:-

Lamp=Q0.0

Memory coil:-

M=Memory bit

PLC program Explanation:-

In network we have considered two digital inputs for two switches S1 and S2. So we have taken NO contact of S1 (I0.0) in series with S2 (I0.1) for AND operation. So when both are ON, memory bit (M0.0) will be ON.

In network 2 we have taken NO contact of memory bit (M0.0) to operate lamp (Q0.0).

Basic fundamental of NO contact and NC contact

Application:-In electrical panel, operate green lamp with NO contact of relay and operate red lamp with NC contact of relay. Write PLC program using ladder diagram language.

 

Diagram:-Basic operation Machine ON lamp and OFF lamp electrical wiring diagram in the panel.

As shown in figure consider two lamps, red lamp is for machine OFF and green lamp is for machine ON. Once relay will get 24v dc machine ON signal, relay will be ON and green lamp will be ON. We have taken here NO contact for green lamp so supply will pass from C to NO as show in figure and if relay is OFF, supply will pass from C to NC so red lamp will be ON.

Components:-24V dc red lamp, 24V dc green lamp, 24V dc relay, wires, 24V dc source, Programmable Logic Controller

PLC program:-

We can write this logic in PLC also. We can use any PLC for this logic. For logic purpose consider Memory coils and outputs.

M coil:-

M0.0 (NO) =Green lamp ON

M0.0 (NC) =Red lamp ON

Outputs:-

Q0.0=Machine command

Q0.1=Green Lamp

Q0.2=Red lamp

 

PLC program:-

We can write this logic in PLC also. We can use any PLC for this logic. For logic purpose consider Memory coils and outputs.

PLC program explanation:-

In network 1 we have taken NO contact of machine command (Q0.0) so when machine command is ON, green lamp (Q0.1) will be ON.

In network 2 we have taken NC contact of machine command (Q0.0) so when machine is off, red lamp (Q0.2) will be ON.

Motor Start/Stop operation with trip indication lamp

Application:-There is one machine in the factory, we want to start/stop motor using push button g from the panel. Give motor ON lamp and motor trip lamp on the panel. When motor is running ON lamp should be ON and if motor trip due to some problem, trip lamp should be ON. Write the PLC program in LAD and FBD language.

Solution:-Here we will make PLC program in the PLC so operator can operate motor from the panel and get indication on the panel. And also we will take inputs signal and outputs for our application

Diagram:-

 

PLC Program:-Write the PLC program from above application using LAD diagram language.

PLC program explanation:-

As per our application we wrote PLC program. In this program we have considered following inputs and outputs for our application. We can use any make PLC for our application.

Inputs:-

Start Button:-I0.0

Stop Button:-I0.1

Trip Input:-I0.2

Outputs:-

Motor:-Q0.0

Motor On Lamp: Q0.1

Trip Lamp:-Q0.2

Network 1:-In this network we are starting and stopping motor by push button. By pressing Start (I0.0) motor can be started and by pressing stop PB (I0.1), motor (Q0.0) can be stopped.

Network 2:-In this network we wrote the logic for motor ON lamp or indication (Q0.1). SO when motor is running, Motor ON lamp is also ON.

Network 3:-For safety purpose we have considered here trip lamp (Q0.2). So when trip signal (I0.2) is ON, trip lamp is also ON.

Analog signal concept

Selecting Analog Sensors: 0-10 VDC, 4-20mA, and 0-20mA

This guide explores the fundamental concepts behind selecting analog sensors with voltage and current outputs for Programmable Logic Controller (PLC) systems. We will delve into the distinctions between these signal types and provide clear guidelines for their application.

What You Will Learn:

• Understand the core concepts of voltage and current sensor feedback.

• Differentiate between voltage and current input signals in industrial applications.

• Explore the reasons for preferring 4-20mA signals over 0-20mA signals.

• Learn why current signals are often favored over voltage signals for analog feedback.

• Gain straightforward guidelines for selecting analog output straight position sensors.

Understanding Analog Output Position Sensors: Voltage vs. Current

While a wide scope of advanced sensor interface types like fieldbus protocols (e.g., Profibus, EtherCAT) and synchronous serial interfaces are available, direct position sensors with basic analog outputs (0-10V, 4-20mA) still account for a significant portion (approximately 66%) of all straight position sensors sold.

When selecting a basic analog output position sensor, your choice typically narrows down to a straightforward voltage signal (e.g., 0 to 10 VDC) or a basic current signal (e.g., 4 to 20 mA or 0 to 20 mA). Let's examine the characteristics of each.

Selection of 0-10 VDC Sensors in PLC Systems

The 0-10VDC signal is a widely recognized and commonly used sensor interface in industrial automation.

Advantages of 0-10 VDC Sensors:

• Widespread Compatibility: It is a ubiquitous standard, readily accepted by almost every modern PLC or industrial controller.

• Ease of Troubleshooting: Its direct voltage measurement often makes it simpler to troubleshoot with a standard multimeter.

• Simplicity: Conceptually, it's a straightforward signal type.

Disadvantages of 0-10 VDC Sensors:

• Vulnerability to Electrical Noise: All analog signals are susceptible to electrical interference. 0-10V signals are particularly vulnerable to noise induced by nearby devices such as motors, relays, and "noisy" power supplies, which can degrade signal integrity.

• Susceptibility to Voltage Drop: Over long cable runs, the 0-10V signal can experience significant voltage drops due to wire resistance. This leads to inaccurate readings at the PLC input, as the voltage arriving at the controller will be lower than that at the sensor output.

Selection of 4-20mA or 0-20mA Sensors in PLC Systems

Current-based signals like 4-20mA and 0-20mA are generally more robust for industrial environments.

Advantages of 4-20mA/0-20mA Sensors:

• Enhanced Noise Immunity: Current signals offer superior immunity to electrical interference compared to voltage signals. This is because current loops are less affected by voltage fluctuations or noise picked up along the cable.

• Reduced Signal Loss over Long Distances: Current signals are less susceptible to signal degradation and voltage drops over long cable runs. The current remains relatively constant throughout the loop, ensuring accuracy at the receiver end regardless of wire resistance (within the loop's compliance voltage limits).

• Wider Controller Acceptance: Increasingly, modern industrial controllers and PLCs are designed to readily accept current signals, recognizing their inherent advantages.

Specific Advantages of 4-20mA over 0-20mA:

The 4-20mA signal provides a significant advantage over the 0-20mA signal due to its "live zero" or "bumble condition area" capability.

• Built-in Fault Detection: With a 4-20mA signal, a 0% measurement (e.g., zero position) is represented by a 4mA current. If the signal ever drops to 0mA, it unambiguously indicates a fault condition, such as a broken wire, sensor failure, or power loss. This allows for immediate fault detection and system safety.

• Clear Zero Indication: The sensor is still actively providing a signal even at its lowest measured value. This is a critical distinction from a 0-10V sensor, where 0V could mean either a true zero measurement or a complete sensor failure, making fault detection more ambiguous.

Disadvantages of 4-20mA/0-20mA Sensors:

• Slightly Higher Cost: Historically, 4-20mA sensors could be marginally more expensive than their 0-10V counterparts. However, this cost differential is continuously decreasing as more sensor manufacturers integrate current-output capabilities as a standard feature.

• More Complex Troubleshooting (initially): While robust, troubleshooting current loops can sometimes require a different approach or specialized tools compared to simple voltage checks.

Why Use Current Signal Instead of Voltage Signal?

In summary, current signals (like 4-20mA) are generally preferred over voltage signals (like 0-10V) for analog feedback in industrial environments due to their:

1. Superior Noise Immunity: Less affected by electromagnetic interference.

2. Reliability Over Distance: Minimal signal degradation over long cable runs.

3. Built-in Fault Detection (especially 4-20mA): The "live zero" allows for clear distinction between a true zero measurement and a system fault.