What is an Interlock?

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⌚Timestamps:
00:00 - Intro
00:50 - What is an Interlock?
01:10 - Types of interlocks
01:20 - A: Safety interlock
02:05 - B: Non-safe interlock
02:13 - Types of non-safe interlocks
02:22 - 1) Mechanical
04:00 - 2) Electrical
05:12 - 3) Logic
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Interlocks are defined as a way to prevent something from happening in a system.
A simple example of an interlock is pushing the brake pedal or clutch in your car before shifting it into drive or first gear. You need to press on the brake pedal to release the shifter into the drive position to prevent the car from lurching forward.
There are two main types of interlocks: safe and non-safe.
Some systems require safe and non-safe interlocks to create a control system. These interlocks prevent people or things from receiving harm while the machine is running.
For example, a safety fence on a robotic cell keeps people out of the cell to protect them from contact with moving objects. When the fence gate of the cell is opened the safety circuit cannot be reset because the circuit is waiting for the gate to be closed. This prevents a person from walking into a robot cell while the robot is running.
The other main type of interlock is a non-safe interlock. These are used to protect equipment or unintended operations.
There are three different kinds of non-safe interlocks. These types of interlocks can be mechanical, electrical, or logic interlocks.
A mechanical interlock is an interlock that is physically connected to another device to prevent unintended actions.
An electrical interlock is an interlock that is used to restrict current flow between two or more devices. These types of interlocks use normally open and normally closed contacts to prevent another device from turning on.
A logical interlock has an instruction or variable which has to be true to allow a result. Logical interlocks are useful when the devices are not easily connected electrically or mechanically.
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You might want to review two of our other articles:
What is a Safety PLC? realpars.com/safety-plc
Motor Starter Explained | Motor Starter Types realpars.com/motor-starter
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[@PulpyButtGoo]

Thank you for taking the time to make these videos! I relied on them a lot as a controls intern, and I have since been offered a full time position after I graduate. I look forward to reviewing certain videos to get back up to speed once I start work. People like you help others more than you know! Keep up the great work

[@realpars]

That's amazing to hear, Andre! Thanks for sharing that.

[@CATSUPPORT]

Thank You Real Pars! your video explaining interlock is extremely easy to understand for a newbie to PLC programming like me. Great video!

[@realpars]

Glad it was helpful!

[@michaelwilliams4086]

The starter kit looks very tempting to make the first move into hands on learning. Thanks for another helpful tutorial

[@realpars]

It certainly is! Glad to hear that the video was helpful. Feel free to leave us any questions

[@MrChDennys]

3:02 It will damadge the contactor and wires before it. It will shortcut A and C phase. PS The motor survives the situation ;)

[@SrOsvaldo1]

Thank You Real Pars!

[@realpars]

Our pleasure, Osvaldo!

[@EP_1990]

Clear and easy to understand. Thank you.

[@realpars]

You are welcome!

[@acectrl]

Thanks for the great video! Well done!

[@realpars]

Our pleasure!

[@kiranchoudhari4717]

Big fan off you realpars team,, thanks for your support team

[@realpars]

Thanks for your support, Kiran!

[@javierferrer4634]

Thank you for sharing this video! Interesting topic! I liked a lot.

[@realpars]

Glad you enjoyed it, Javier!

[@IngDzib]

Thanks, wonderful video!

[@realpars]

Glad you enjoyed it!

[@sebastiannielsen]

About the steering wheel example at 3:05, the key is NOT the interlock, rather the construction of the core in the ignition switch is the interlock, which prevents the car from starting, unless you have unlocked the anti-theft device of the steering wheel. The mechanical design is such as, so if the steering wheel lock lug have jammed, the core design will not allow the vehicle to start. Another interlock design is that the anti-theft lug will not engage unless you physically pull out the key because of 2 interlocking lugs in the keyhole interfering with the anti-theft lug. This is an important safety feature, as it allows you to turn off the car in an emergency (for example, motor runaway or throttle lockup) without also hindering your ability to steer the car. The anti-theft lug is also interlocked in such a way, its impossible for it to engage while the car is running, even if the key-out interlock would in some way fail. The key WOULD be the interlock, if you for example had a garage port, that requires the ignition key (or another key or peg or similiar that is on the same keyring as the ignition key) to be inserted to be closed, and will not release the ignition key until fully open. Some commercial truck garages have this function to prevent a truck from driving through the closed port. Of course, this means when the garage is not in use, the port stay open, but then theres nothing in the garage. I would say the definition of interlock is "a method of restricting an action which would interfer with another action" - "interfer" here would mean either physically as with the pneumatic cylinders example, but also logically for example with robots interfering with human operations or the engine of car interfering with the movement of car during shifting unless brake is depressed, and another thing to qualify for being a interlock is that it must be both ways, if the interlock prevents B from being started while A is running, then it must prevent A from starting while B is running. In the example with the motors on conveyor belts, to qualify for a interlock, the motors would also need to have a function that shuts off motor 1 if motor 2 or 3 stops, and shuts off motor 1 and 2 if motor 3 stops. (or prevents them from being stopped in the wrong order, but then you would need to have a completely different E-stop circuit that have the ability to fire the E-stop of the upstream motors if the E-stop of a downstream motor is pushed. If you instead have a logic condition to stop upstream motors when downstream motors stop for any reason, then a downstream E-stop would automatically call for a logic stop of upstream motors - which for safety reasons wouldn't count as a E-stop of the upstream motors, but since theres no emergency at the upstream motors, a logic stop is permitted by safety standards.)

[@realpars]

Thank you for sharing your knowledge and experiences, Sebastian! We truly appreciate that.

[@copernicus6420]

What a beautiful explanation. I subscribed

[@realpars]

Awesome, thank you!

[@carlosexchangehd4631]

thanks for the inf man ! well done !

[@realpars]

Glad it was helpful, Carlos!

[@dotex2809]

Great as always !

[@realpars]

Thanks a lot!

[@allezvenga7617]

Thanks for your sharing

[@inothome]

I know you like the videos to be 100% accurate, on the motor interlock example starting at 6:42, the first rung, parallel branch, you have Motor_3_Start, not the Motor_3_Relay on the parallel branch. Great video as always!

[@realpars]

Thanks for your support!

[@CATSUPPORT]

yep, this video very very great

[@shamimahappy6455]

Great Explanation

[@realpars]

Glad it was helpful!

[@jordaz87]

great video

[@mantiyaz1]

Thanks for share 👍🏽👍🏽

[@jimbass924]

Great video!

[@realpars]

Glad you enjoyed it, Jim!

[@aminokamad1681]

Awesome video sir 🔥🔥🔥

[@realpars]

Thank you, Amin!

[@mohammadshafiullakhan5604]

Thank you so much for the 👍👍👍great video

[@realpars]

You're welcome!

[@juanlorenzo5501]

Thank you for information

[@realpars]

Our pleasure!

[@andressilva2402]

This is a great video. Was wondering if there's a video on how a automation panel is wired up for example from power coming in to powering devices such as drives, contactors and relays. I always have trouble knowing what powers what

[@realpars]

Thanks for your comment, Andres! I will happily pass your suggestion on to our course developers for future video courses. Happy learning!

[@engrbaqar4823]

Thank you sir...Dear sir please make a full video on Medium voltage Switchgear system

[@realpars]

Thanks for your feedback and suggestion! Will surely pass this on.

[@engrbaqar4823]

@@realpars welcome sir

[@graffonthebuilding1135]

Another Amazing Video! Congratulations. But let let me fix a simple little detail, in the Full voltage reversing motor starter, when we have the two contactors activated this will be generate a short-circuit between L1 and L3, I don't see problems with the motor related with this. I'm Tia Portal Programmer then i Love Your Videos!

[@realpars]

Thanks for your support!

[@cdrive5757]

I'm not sure what you're implying. If you're saying that having both FWD and REV Contactors energized won't damage the motor I agree but it certainly plays hell on the Contactors and Breaker Panel.

[@graffonthebuilding1135]

@@cdrive5757 of course, the short circuit will cause the current to tend to infinity, destroying the conduction components if it does not act properly.

[@cdrive5757]

@@graffonthebuilding1135 Infinity is a gross exaggeration. Ohms Law doesn't take a holiday when there's a short circuit! IE ... there's no such thing as absolute zero resistance.

[@graffonthebuilding1135]

@@cdrive5757 if the circuit have a good system for short circuit protection, we all safe!

[@brush_popper]

Thanks I like this video. 💛

[@realpars]

I'm glad you like it!

[@mohamedkouache1288]

very useful

[@realpars]

Glad to hear that!

[@ziaullah8756]

nice video

[@realpars]

Thank you!

[@amrfathi3155]

You are awesome 👌

[@realpars]

Thank you!

[@bunnandjenn9405]

Thanks.

[@realpars]

No worries!

[@thu-alfikarfalih3278]

Beautiful

[@realpars]

Thank you!

[@Ravinder764]

👍👍👍 knowledge

[@marctudor7384]

NICE !!! :D

[@realpars]

Thank you!

[@user-gb6wj6fn9x]

OK, Siemens RS485 coupler - good solution, for example...

[@sultanalmahdaly837]

Can a starter be used as an actual place to operate small equipment

[@realpars]

Sure. When connected to a motor and with the addition of overloads, fuses, disconnects, etc., it is referred to as a motor starter. With just the coil and contact package, it is a contactor and can be used to turn equipment on and off (small motors, power tools, etc.). A contactor is a high-powered relay, available in many capacities from 1A - 200A and above.

[@alaeddinek4599]

So, an interlock can also be named as permissive (eg: permissive to start an export pump needs tank offloading valve to be open and a booster bump to be running) ?

[@realpars]

Hi there, there are synonyms for interlocks, permissives are another way to say the same thing. Hope this helps!

[@fatihkeklik906]

If I get a pro membership, i get a starterkit package without make any other payment right? And I am at Turkey do i can order it here? And how i will order? I get a promotion code and go to siemens website and order starter package with it?

[@realpars]

Hi Fatih, Thanks for your comment! You do not receive a free starter kit package when you enroll in our pro membership. You do, however, receive a discount code for the starter kit once you sign up. You will receive an email with the discount code and explanation after you registered for our Pro Membership. Otherwise, you can purchase the starter kit on its own on our MarketPlace. marketplace.realpars.com/ You can register for our pro membership over here. learn.realpars.com/bundles/pro Hope this helps! If I can be of any further assistance, please let me know - I’m more than happy to help!

[@sjholmesbrown]

The circuit diagram you have drawn for the CR1 CR2 interlock at 4:35 is incorrect. Your narration correctly says you would wire the coil of CR2 in series with the NC contacts of CR1, but the diagram you have drawn shows the _contacts_ of CR2 in series with the NC of CR1. This will prevent the light operating if CR1 is on, but not the actual coil of CR2.

[@realpars]

The video is both correct and incorrect. The narration is descriptively correct, but the circuit to the light bulb is made when the current can flow through the contacts of CR2. This happens when CR1 is de-energized and CR2 is energized. What the diagram should have shown is the separate circuit for the coil and the contacts. The current flow through CR1's NC contact can be wired to the coil of CR2 to energize it. A separate circuit through CR2's NO contact would then light the light when CR2 is energized.

[@kavindumadushan8098]

💜️

[@iamsupercoolish]

sweet

[@chriscockrell9495]

00:00 - Intro 00:50 - What is an Interlock? Preventing actions. Brake or clutch 01:10 - Types of interlocks - safe and non safe 01:20 - A: Safety interlock - prevent people or equipment from harm. Robot cell door lock 02:05 - B: Non-safe interlock 02:13 - Types of non-safe interlocks 02:22 - 1) Mechanical - full voltage forward and reverse motor, key restricts wheels and start, trap key system (trap key safety fence - sequential requirements) 04:00 - 2) Electrical - relays and contactors are electrical interlock, 05:12 - 3) Logic - true. Pump down stream of a process, pressing a button for 3 seconds pnuematic cylinders not colliding conveyor belts motors so packages don't stack up.

[@mechanikalkraken]

Yeah....In S7-1500 GRAFCET Programm have inside this option in every STEP

[@kevin00861]

Thanks a lot, This educational video is the only thing I was looking for to enrich my knowledge about interlocking ... Thanks a lot REALPARS team 🤍

[@realpars]

You are most welcome! Glad to read such positive feedback, Malik!