What Is an Off Delay Timer?
The off delay timer is a common device used in industrial automation and control systems. It provides flexibility and control in a wide range of applications.
When the coil of the timer is energized its contacts change position; normally open contacts will become closed and vice versa. The contacts remain in the changed state until the timer is de-energized.
Timer Relay Setting Interface
Many times in a control panel a device or system may need to wait for an amount of time before it’s allowed to continue. This is where an off delay timer relay can help. These devices can be found in a variety of applications, most commonly in commercial and industrial areas. They may control motors or other equipment in a laundry mat, car wash or any other application that needs the power to continue after an amount of time.
The setting interface for a timer is usually done through a dial or switches on the front of the device. There are both digital and analog settings available, but the most common is a digital interface where you can simply press a button to set the device. Some devices also have a display that lets you know how long your desired delay will be.
One of the most popular types of timers is the single shot type. This device will accept a trigger and will then remain energized for the pre-set duration of time. The only way the device will de-energize is if another trigger is provided before the time out period ends. Other types of timers include the repeat cycle and watchdog type. These are primarily used to sequence a series of on and off contacts over a certain period of time.
Normally Closed Contact
When the normally closed contact of an off delay timer is pressed it will close and turn on the output. The circuit will stay on until the timer is reset by removing power from the coil or a preset amount of time passes. This allows things like extract fans to keep running in kitchens for a short time after the push button is turned off to allow fumes to escape the room.
Normally closed contacts or switches are used extensively in electrical hot swap controller ic systems and you will find them in switches like start buttons, reset buttons, and even on light switches. You will also use them in a wide variety of industrial processes. They are also commonly used in emergency shutdown systems to ensure that a process has stopped before allowing power back on.
Ladder diagrams will show timed contacts with an arrowhead pointing in the direction of the timing action. This indicates that the contact will change from its normal state to its timed position only when the timer coil is activated and the accumulated off delay time equals the predetermined delay. Once this happens the timer coil will de-energize and the timed contacts will return to their normal position.
You will need to know whether the contacts in a system are normally open or normally closed when working on it. This information can typically be found in a manual or by looking at a schematic. In most cases, the contact will be labelled as such (NO or NC) but if you are not sure check a wiring diagram to get more information.
Normally Open Contact
There are many different functions a timer can perform but they all come down to two basic types of timing functions, on delay and off delay. The on-delay function has a contact that goes from its normal state to an on state when the timer coil is energized and stays in the on state for a preset amount of time. The off-delay function has a contact that changes from an open state to a closed state when the timer coil is energized. The off-delay contact stays in the open state for a preset amount of time and then reverts back to its original state.
In most cases the contacts of a timer will have markings on them that indicate what type they are, but not always. If no markings are present you can test a timer with a multimeter to find out what state the contact is in when not energized.
The off-delay timer has a coil that is designated like all other loads in ladder diagrams with the exception of the abbreviation TD to denote time delay. The contacts resemble single pole switches and have an arrow pointing downward from them. Normally open off delay contacts are also known as normally open timed open contacts and a normally closed off delay contact is called a normally closed time close contact. Unlike other electrical timers the light driver off delay timer’s contacts change their states instantly when the coil is energized and then delay when they are de-energized.
Time Delay
Often used in industrial applications, this timer relay allows you to set up your control system to delay the energized state of an output signal until after a certain amount of time has passed. The OFF delay timer also known as a sleep delay timer or an off delay relay is ideal in situations where you need to deactivate a signal after it has already been activated.
Upon initial application of input supply or trigger, the output contacts transfer – connecting (normally open) or disconnecting (normally closed). The timer starts counting, and once the set time has been reached, the timer will remain energized until the OFF delay count reaches zero.
The off delay timer has the ability to be reset, but this is not required in most applications. The reset button is located on the back of the timer relay, and when pressed the output contacts change states. This resets the timer and it will begin counting again.
This type of timer is commonly found in Star-delta starters, capacitive load starters and other similar applications. A key difference between an on delay timer and an off delay timer is that the on delay has instantaneous contacts. Unlike the OFF delay, which counts from when the coil is energized, an ON delay timer will only start the count once the rung input goes false.
