I would like to hear some examples?

 

Well you are being very vague in your question but an interlock is anything that does not allow a device to run/turn on etc. unless certain conditions are met. An example would be say a limit switch on a valve indicating an open position is wired in series to a pump starter so until the valve is open the pump would not be allowed to run. Need more info but that is just one example.

 

We use interlocks extensivly to comunicate information between equipment: An assembly line presents parts to a unload area, a robot picks up the parts from the unload area and loads them into racks presented by a rack handlind system, the rack handling system moves and stacks the racks making them ready to be picked up by a lift truck. All of these signals could be sent and recieved by most any method but we have found that wires between for these important signals work much better than any other method we've tried. The assembly line turns on an output (ready for pickup --> robot), the robot starts to run its program and sends a signal back to the assembly line which shuts off the ready signal until the next part is in place, when the rack is ready for a part it sends a signal to the robot allowing the robot to load its part, the robot sends a signal to the rack handling system when it is done and the rack handling system can move or index getting ready for the next part. Wow, that was wordy but that is exactly how we do it.
Interlocks work well when you have two way hand shaking to be certain the information got there and was acted on.

 

An interlock is a condition or series of conditions that must be met to allow an operation or process to continue. Examples are numerous, but some general examples include:

shield interlock- the machine cannot run unless all the safety shields are closed

flow interlock - the operation cannot continue unless the coolant flow is adequate

pressure interlock - the operation cannot start unless adequate air or hydraulic pressure exists.

level interlocks - the pump cannot run if the tank level is too high or too low.

presence interlock - an operation cannot start until a part is detected in the work station.

The term is often used loosely and can refer to a phsical device (such as a switch, sensor, or meter), or a control circuit, or a sofware construct, or a specific function. Another common term is "permissive," although permissvie is usually, but not always, more limited to software references.

 

In a multi process application an interlock indicates that one process is put on hold to let another thread finish a job first.

Both process A and B can be running simultanuously, but at a certain point in the process A it needs to wait for process B to finish an action. Process A is stopped (locked) until B finishes and only when B gives A feedback to indicate it has indeed finished, process A resumes. Interlock= a lock between to processes to ensure the correct order of actions...or something like that

Stuff like this is common in complex C++ applications where multi threading is used.

Hope this helps.

 

An interlock is a device which prevents simultanious operation of conflicting parts.

 

The term "interlock" has many usages in industry.

The ISA definition of an interlock is:

interlock
1. To arrange the control of machines or devices so that their operation is interdependent in order to assure their proper coordination [RP55.1].
2. Instrument which will not allow one part of a process to function unless another part is functioning.
3. A device such as a switch that prevents a piece of equipment from operating when a hazard exists.
4. To join two parts together in such a way that they remain rigidly attached to each other solely by physical interference.
5. A device to prove the physical state of a required condition, and to furnish that proof to the primary safety control circuit.

Source: The Automation, Systems, and Instrumentation Dictionary, 3rd ed, ISA

Examples:

Switches that are mechanically interlocked so that the switches cannot be in the same position at the same time such as an up/down switch combination where the up and down cannot be on at the same time.

A valve may be interlocked to prevent it from being open when another valve is open.

Mechanical, electrical, or logic means that assure coordinated operation between different parts of a machine

Mechanical, electrical, or logic means that assure coordinated startup and shutdown of group of machines.

Another term that is sometime used interchangeably with interlock is "permissive" but in reality a permissive is a subset of "interlock."

Permissive - logic that prevents a sequence of operation or events from proceeding unless the conditions of the permissive are met. Examples of this are:

On fired equipment, that the pilot cannot be lit unless the purge cycle is complete.

A material is prevented from being added to a batch process until the batch has been agitated for a period of time.

Another term that interlock is used sometimes used interchangeably with is Emergency Shutdown systems which is again probably a subset of "interlocks."

Emergency Shutdown system(ESD) - a system designed to take a process to a safe state when certain conditions occur.

Examples of this are a reactor over pressure system that upon exceeding a set pressure, the reactor is vented or on low level in a tank the discharge pumps are stopped and the outlet is blocked.

These days the generic term for all of these that are safety related that are electrical, electronically, or programmable electronic system(PES) based is Safety Instrumented System(SIS) which comes from ANSI/ISA 84.01 and IEC d61511.

Bill Mostia
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William(Bill) L. Mostia, Jr. P.E.
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exida.com, LLC
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These opinions are my own and are offered on the basis of Caveat Emptor.

 

An interlock is a condition or series of conditions that must be met to allow an operation or process to continue. Examples are numerous, but some general examples include:

shield interlock- the machine cannot run unless all the safety shields are closed

flow interlock - the operation cannot continue unless the coolant flow is adequate

pressure interlock - the operation cannot start unless adequate air or hydraulic pressure exists.

level interlocks - the pump cannot run if the tank level is too high or too low.

presence interlock - an operation cannot start until a part is detected in the work station.

The term is often used loosely and can refer to a phsical device (such as a switch, sensor, or meter), or a control circuit, or a sofware construct, or a specific function. Another common term is "permissive," although permissvie is usually, but not always, more limited to software references.

What is communication interlock for an automated application?

 

Could be that a communication channel must be present or available for some action to proceed.

Or a communication channel is disabled (interlocked) under certain conditions, probably to allow a higher priority communications channel to operate.

Tough to tell out of context.