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Oct 20 2020

Time Delay Relay Basics: Relay Circuit and Applications

Introduction

Time relay refers to a kind of relay whose output circuit needs to make an obvious change (or contact action) after adding (or removing) the input action signal in a specified and accurate time. It is an electrical component used in a circuit with a lower voltage or a smaller current to switch on or off a circuit with a higher voltage and larger current. With the development of electronic technology, electronic time relays have become mainstream products in time relays. Electronic intelligent digital display time relays using large-scale integrated circuit technology have many working modes, which can not only achieve long delay time, but also have high time delay accuracy, small size, convenient adjustment and long service life, making the control system simpler and more reliable. The time relay also has the function of automatic monitoring. Time relay and other equipment together can form a program space route to realize the automatic operation of the equipment.

Time Relay Basics Explained

Catalog

Introduction

Ⅰ Time Relay Basics

1.1 What is a Time Delay Relay?

1.2 Time-delay Relay Working Principle

1.3 Timer Relay Structure

1.4 Timer Relay Parameters

1.5 Four-type Time Relay Contacts 

Ⅱ Understanding Time Delay in Relay Circuit

Ⅲ Time Relay Classifications

3.1 According to Working Principle

3.2 According to the Delay Modes

Ⅳ How to Wire Time Relay?

Ⅴ Time Relay Applications

Ⅵ Time Relay Selection

Ⅶ Timer Relay Using Instructions

7.1 General Ideas

7.2 Two Points for Attention in Using Time Relays

Ⅷ Case Study: Time Relay Switch in Light Circuit


Ⅰ Time Relay Basics

1.1 What is a Time Delay Relay?

The time relay is a very important component in the electrical control system. In many control systems, use the time relay to achieve delay control. Time relay is an automatic control electrical appliance that uses the principle of electromagnetic or mechanical action to delay the closing or opening of contacts. Its characteristic is that there is a delay from the time the attracting coil gets the signal to the action of the contact. The time relay is generally used to control the motor starting process with time function.

As above mentioned, the main function of the time relay is as an executive device in simple program control. When it receives the start signal, it starts timing. After the timing ends, its working contact opens or closes to promote the subsequent circuit work. Generally speaking, the delay performance of the time relay can be adjusted within the range of design, so as to facilitate the adjustment of its delay time. In addition, a time relay alone may not be able to do close. After closing for a period of time, it will open again. It is a cycle of time-delay closing and opening. However, configuring a certain number of time relays and intermediate relays can do it.

 

1.2 Time-delay Relay Working Principle

Time relay is widely used in remote control, telecommunication, automatic control and other electronic equipment, and is one of the most important control components. When the coil is energized, the armature and the pallet are attracted by the core and move down instantaneously, making the action contact close or open. However, the piston rod and the lever cannot fall with the armature at the same time, because the upper end of the piston rod is connected to the rubber film in the air chamber. When the piston rod starts to move downward under the action of the release spring, the rubber film is concave downward. The air in the air chamber becomes thinner, causing the piston rod to be damped and slowly descend. After a certain period of time, the piston rod descends to a certain position, and then the delay contact action is pushed through the lever to make the moving contacts open and close. The time from when the coil is energized to when the delay contact completes the action is the delay time of the relay. The length of the delay time can be changed by adjusting the size of the air inlet hole of the air chamber with a screw. After the suction coil is de-energized, the relay relies on the spring to recover. And the air is quickly expelled through the air outlet.

 

1.3 Time Relay Structure

Air-damping Time Relay

Figure 1. Air-damping Time Relay

1 Coil

5 Push plate

9 Weak Spring

13 Adjusting Screw

2 Iron Core

6 Piston rod

10 Rubber Film

14 Air Inlet

3 Armature

7 Lever

11 Air Chamber Wall

15 Micro Switch

4 Reaction Spring

8 Spring

12 Piston

16 Micro Switch

 

1.4 Time Relay Parameters

Technical parameters include rated voltage, contact working current, contact type and quantity, delay time, accuracy, ambient temperature, mechanical life and electrical life, etc. Now take SJ23 series air-type time relay as an example, its technical parameters are as follows:

1) Rated control capacity: AC300VA, DC60W (30W delay contact assembly).

2) Rated voltage level: AC380V, 220V; DC220V, 110V.

3) Rated voltage of the coil: AC110V, 220V and 380V.

4) Maximum operating current of the contact: 0.79A at AC380V, 0.27A (momentary) and 0.14A (delay) at DC220V.

5) Delay repeat error: ≤9%.

6) Hot-state pull-in voltage: no more than 85% of the rated voltage of the relay. When the voltage drops from the rated value to 10% of the rated value in cold-state, it can be reliably released. And it can reliably release after reaching 110% of the rated voltage.

7) The mechanical life is not less than 1 million times, and the electrical life is 1 million times (the DC life of the delay contacts assembly is 500,000 times).

 

1.5 Four-type Time Relay Contacts

Time Relay Symbols

Figure 2. Time Relay Symbols

NOTC (normally-open, timed-closed): When the coil is not energized, the NOTC contact is normally open. It is closed by energizing the relay coil, but only within a specified time after the coil is continuously energized. The moving direction of the contact (close or open) is the same as that of a standard normally open contact. Since the delay occurs in the direction in which the coil is energized, this type of contact is normally open and on-delay. NOTO (normally-open, timed-open): Unlike the NOTC contact, the timed action occurs when the coil is de-energized. Since the delay occurs when the coil is de-energized, this type of contact is normally open and off-delay.

NCTO (normally-closed, timed-open): When the coil is not powered on, the NCTO contact is normally closed. By energizing the relay coil, the contact is opened, but only within a specified time after the coil is continuously energized. The movement direction of the contact (closed or opened) is the same as the standard normally closed contact, but there is a delay in the opening direction. NCTC (normally-closed, timed-closed): The NCTC contact is similar to NCTO contact, because when the coil is normally closed when in de-energized and opened by energizing the coil.

 

Ⅱ Understanding Time Delay in Relay Circuit

Set delay time of a relay. Generally speaking, the delay performance of the time relay can be adjusted within the range of design, so as to facilitate the adjustment of its delay time in circuit. 

Time Delay Relay Circuit (Power-Off)

If you are using an on delay relay, the delay will start immediately after the input signal is obtained. After the delay is completed, the executive part will output the signal to the control circuit. When the input signal disappears, the relay will immediately return to the pre-action status. It is opposite to an off delay relay. When the input signal is obtained, the execution part immediately has an output signal. After the input signal disappears, the relay needs a certain time to restore to the state before the action.

timer relay structure

Figure 3. Timer Relay Structure

Ⅲ Time Relay Classifications

3.1 According to Working Principle

According to different working principles, time relays can be divided into air damping time relays, electric time relays, electromagnetic time relays, electronic time relays, etc.

(1) Air damping time relay

The type is obtained by using the principle of damping when air passes through the small hole. Its structure is composed of three parts: electromagnetic system, delay mechanism and contact. The electromagnetic mechanism is a double-port direct-acting type, the contact system is a micro switch, and the delay mechanism adopts an air bag damper.

(2) Electronic time relay

Utilize the principle that the capacitor voltage in the RC circuit can't jump, and can only change gradually according to the exponential law, that is, the delay is obtained by electrical damping characteristics.

Features: Wide delay range, high precision (generally about 5%), small size, shock resistance and easy adjustment.

(3) Electric time relay

Use the miniature synchronous motor to drive the reduction gear train to obtain the time delay.

Features: The delay range is wide, up to 72 hours, and the delay accuracy can reach 1%. At the same time, the delay value is not affected by voltage fluctuations and environmental temperature.

Its delay range and accuracy are unmatched by other time relays. Its disadvantages are complex structure, large size, short life, high price, and accuracy is affected by the power frequency.

(4) Electromagnetic time relay

Use the principle of slow attenuation of the magnetic flux after the electromagnetic coil is cut off to delay the release of the armature of the magnetic system to obtain the delay action of contacts. It is characterized by large contact capacity, so the control capacity is large. However, the delay time range is small, and the accuracy is slightly worse. So it is mainly used in the control of DC circuits.

 

3.2 According to the Delay Modes

Based on it, time relays can be divided into two types: on-delay type and off-delay type.

(1) The on delay type time relay starts to delay immediately after receiving the input signal. After the delay is completed, its execution part outputs the signal to manipulate the control circuit. When the input signal disappears, the relay immediately returns to the state before the action.

on delay relay

(2) The off delay type time relay is just the opposite. When the input signal is obtained, the execution part immediately has an output signal. After the input signal disappears, the relay needs a certain delay to restore to the state before the action.

off delay relay

 

Ⅳ How to Wire Time Relay?

The time relay is a very important component in the electrical control system. There are power-on delay type and power-off delay type. Based on action type, there are electronic type and electric type, etc. Between them, the electronic type uses the principle of capacitor charging and discharging combined with electronic components to achieve delay action. There are many electric styles by using airbags and springs.

time relay wiring schematics

Figure 4. Time Relay Wiring Schematics

Time Relay Wiring:

1) Control wiring: Consider it as a DC relay.

2) Work control: Although the control voltage is connected, whether it plays a control role is determined by the timer on the panel.

3) Function understanding: It is a switch,single-pole double-throw, with an active point, just like the active arm of a common knife switch.

4) Load wiring: Connect the neutral wire of the power supply or the negative terminal .

5) Working principle: When the timer is invalid, it is equivalent to the normal light in the switch-off state. When timing, the relay will act and the electrical appliances will be energized to work, which is equivalent to the normal lightinthe switch-on state.

Take the power-on delay time relay as an example:

on delay relay contacts

Figure 5. On Delay Relay Contacts Wiring

 

Ⅴ Time Relay Applications

In Flash Control

  • Two time relays cooperate with each other to provide constant frequency on/off pulses of the contacts, sending intermittent power to the light.  

In Furnace Safety Purge Control

  • Before the combustion furnace can be safely ignited, the fan must run for a certain period of time to clean out any flammable or explosive steam in the furnace chamber. The time relay provides the required time parts for the furnace control work.

In Electric Soft-start Delay Control

  • It is not necessary to start a large electric engine by switching full power from a completely stopped state, and can reduce voltage softly start with less inrush current.

In Conveyor Belt Sequence Delay

  • When multiple conveyor belts are arranged to transport materials, the conveyor belts must be started in the reverse order (the last one is first, the first one is last) to prevent materials from accumulating on the moving conveyor which may be stop or move slowly.

 

Ⅵ Time Relay Selection

The selection of time relay is mainly due to delay mode and parameter coordination. The following aspects should be considered when selecting.

(1) Delay mode selection

It should be selected according to the requirements of the control circuit. The reset time after the action is longer than the inherent action time, so as to avoid misoperation, or even no delay. This is especially important in the occasions of repeating delay circuits and frequent operations.

(2) Type selection

For occasions where the delay accuracy is not high, cheaper electromagnetic or air damping time relays are always used. On the contrary, for occasions where the delay accuracy is high, electronic time relays can be used.

(3) Coil voltage selection

According to the voltage of the control circuit, the voltage at which the relay attracts the coil is selected.

(4) Selection of power supply parameters

In the occasions where the power supply voltage fluctuates greatly, it is better to use air damping or electric time relays than the transistor type. And in the occasions where the power frequency fluctuates, electric time relays should not be used. In addition, when the temperature changes greatly, air damping type should not be used.

When selecting a time relay, pay attention to the current type and voltage level of its coil (or power supply), and other factors, such as delay mode, contact form, delay accuracy and installation method according to the control requirements.

timer relay

Ⅶ Timer Relay Using Instructions

7.1 General Ideas

1) Keep the time relay clean, otherwise the error will increase.

2) Before use, check whether the power supply voltage and frequency are consistent with the voltage and frequency of the time relay.

3) Choose the control time of the time relay according to user requirements. Regardless of the type of time relay, as long as the timing time is equal to the set time, its output contacts will act to achieve the purpose of timing control circuit.

4) For DC products, pay attention to wiring according to the circuit diagram and pay attention to the polarity of the power supply.

5) After the time relay is out of working state, it should be reset immediately for the next use. If the repeated use interval is less than the reset time, the control circuit will be abnormal. What’s more, the power-on delay type is automatically reset after power off; and the power-off delay type is automatically reset after power on.

6) Try to avoid using it in places with obvious vibration, direct sunlight, humidity and oil contact.

 

7.2 Two Points for Attention in Using Time Relays

  • Three Key Points

1) Starting point of timing

On one hand, when selecting the timing point of the power-on delay time relay, you should choose to supply power to the time relay when the timing signal is sent by the control circuit that needs to perform timing. On the other hand, when selecting the timing point of the power-off delay type time relay, you should choose to cut off the power supply of the time relay when the control circuit that needs to send out the timing signal, so that the timing can be performed.

2) Ending point of timing

The timing end point has two meanings: one refers to the point at which the set time is equal to the timing time; the other refers to the point at which the contact operates.

3) Reset point of timing

The reset of the time relay is to clear the last timing content for the next use. If it is not reset, an abnormality will occur the next time it is used. Special attention should be paid to: the interval between two uses should be greater than the reset time, which is particularly important in electric time relays.

 

  • The relationship between the starting point, ending point and reset point of timing

1) After the time relay is used, there is a reset problem. Therefore, most of the control circuits are in the next level circuit by the time relay output. After the timing completion signal is accurately obtained, it is used to cut off the power supply of the time relay (power-on delay type), or power the time relay (power-off delay type).

2) In the upper and lower control circuits of the time relay, there are components that cannot work at the same time. If the time relay cannot accurately operate of the upper and lower control circuits at these points, it will cause the device to operate abnormally.

 

Ⅷ Case Study: Time Relay Switch in Light Circuit

Control requirements: Light 1 and light 2 are on at the same time, and light 2 is off in 30 seconds after light 1 is off. When light 1 is on, light 2 can be off at any time.

According to the control requirements, explain through the following circuit diagram.

time relay application circuit

Figure 6. Time Relay Switch in Light Circuit

1) Press SB2, the contactor KM is energized and self-locked, and at the same time KT is also energized, and KT closes.

2) After KT is turned on, the intermediate relay KA is also energized to work.

3) At the same time, contact KM and contact KA are also closed at the same time, light 1 and light 2 are on.

4) When the stop button SB1 is pressed, the contactor KM powers off, the contact KM opens, and the light 1 is off at the same time. Because of the existence of the power-off delay relay, KT is still on as well as the light 2. It goes out after the timing set by the time relay.

5) When light 1 is on, and contact KA1 is turned on at any time, the time relay resets. KT disconnects and the light off.

This is the typical application of a off delay relay. However, in the actual circuit, the control logic may be more complicated than this, so we must deeply understand the working principle and application of the time relay.

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pinglun 2 comments

    • pingluntus
    • Coxilin on 2020/10/29 15:26:04

    Hi, How do you test a time delay relay?

      • pingluntu
      • author on 2020/10/29 16:00:09
        author

      Re:

      Simple steps for common timer relay test:

      1) Adjust the timer with high time delay for example: 2 minutes.

      2) Energize the relay with 125V and measure the dc current.

      3) Note down the current before timer operates.

      4) After 2 minutes relay will pick up. Note down the current after operation.

      5) Calculate the relay power (W) = 125v x measured current.

    • pingluntus
    • Cocolee on 2020/11/20 17:56:36

    After read it, can you tell me which type of relay is used as time delay relay?

      • pingluntu
      • author on 2020/11/21 9:38:26
        author

      Re:

      On- and off-delay timers represent the most typical time delay relay timers in use. Other types include interval-on-operate, flasher, and repeat cycle timers. Normally open, on-delay timers start timing when the input voltage (power) is applied.

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