ClassX Video Lessons Youtube Channel The Engineering Mindset Time Delay Relays Explained – How timing relays work hvacr
Welcome to an exploration of time delay relays and timer switches, essential components in automation and control systems. This article will guide you through the main types of time delay relays, their functionalities, and their applications, particularly in HVAC systems and industrial settings.
Time delay relays are specialized control relays equipped with a built-in time delay function. They manage events by energizing a secondary circuit after a predetermined time or for a specific duration. Unlike standard relays, which activate immediately upon receiving voltage, time delay relays introduce a delay, allowing for more controlled operations.
There are two primary types of time delay relays:
Both types can be configured as normally open or normally closed, with delay times adjustable from milliseconds to days.
Timing relays are widely used in various applications, including:
For instance, in a workplace corridor, a time delay relay can ensure lights remain on only for a specific period after being switched on, thus saving energy.
Modern time delay relays offer advanced features, including multiple functions and timing ranges. They are available in various forms, such as plug-in devices, circuit boards, and DIN rail-mounted controls. Setting them up is straightforward, often requiring simple adjustments via dials, with no programming needed.
Many relays include an LED indicator to show the current function being performed, as detailed in the manufacturer’s guide.
Consider an outdoor restaurant heater. To avoid excessive energy use, a time delay relay can automatically turn off the heater after a set period, such as 30 minutes, ensuring comfort without waste.
To illustrate, let’s look at a simple circuit with a battery, LED, and switch. By adding a capacitor, we can delay the LED turning off after the switch is opened. The capacitor discharges slowly, keeping the LED illuminated for a while. Adjusting the capacitor size changes the delay duration.
For more precise control, a transistor can be added to act as a switch, allowing current flow only when a specific voltage is applied to its base pin.
In a delay time-on circuit, a zener diode can be used to control when a lamp turns on. The diode blocks current until the capacitor charges to a certain voltage, at which point it allows current to flow, illuminating the lamp.
Such designs are foundational in understanding how timing relays function, providing a visual grasp of their operation.
Time delay relays are versatile tools in automation and control systems, offering precise timing control for various applications. Whether in industrial settings or everyday building services, they enhance efficiency and functionality. For further learning, explore additional resources and videos on electrical and controls engineering.
Engage in a practical session where you will configure different types of time delay relays. Experiment with delay-on and delay-off settings using adjustable dials. This will help you understand how timing adjustments impact relay operations in real-world applications.
Utilize simulation software to model HVAC systems incorporating time delay relays. Observe how these relays manage heating and cooling cycles, and experiment with different timing settings to optimize system efficiency.
Create a simple circuit using a battery, LED, switch, and capacitor to implement a delay-off feature. Adjust the capacitor size to see how it affects the delay duration, and discuss the implications of these changes in practical scenarios.
Analyze a case study where time delay relays are used to conserve energy in building services. Discuss the benefits and challenges of implementing such systems, and propose improvements based on your understanding of relay functionalities.
Work in groups to research and present on the advanced features of modern time delay relays. Focus on multiple functions, timing ranges, and setup processes. Highlight how these features can be leveraged in industrial automation and building management systems.
Sure! Here’s a sanitized version of the provided YouTube transcript:
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[Applause] Hey there, everyone! Paul here from The Engineering Mindset. In this video, we’re going to explore timer delay relays and timer switches to understand their main types, how they work, and where we use them.
Telecontrols has kindly sponsored this video. They are a leading manufacturer in the automation industry since 1963, offering some of the best timers on the market with a wide range of functionalities and time ranges. Be sure to review their time delay relay portfolio along with suitable relay bases and accessories. You can contact them at salestelecontrols.com or via LinkedIn to learn more. Simply click the link in the video description below.
Time delay relays are control relays with a built-in time delay function. They control an event by energizing the secondary circuit after a specified amount of time or for a given duration. Some can even do both. In a standard normally open control relay, the contacts on the secondary side close immediately when voltage is applied to the coil on the primary side. When the electricity is cut on the primary side, the contacts on the secondary side open and cut the power to the load.
For some applications, we do not want an immediate response on the secondary side; we want this to occur after a certain amount of time or only for a specific duration. For this, we can use a time delay relay. There are two main types of basic timing relays: the delay-on type and the delay-off type. These can be normally open or normally closed relays, and we can control the delay time from milliseconds to hours or even days.
By the way, we have covered the basics of mechanical relays in detail in our previous video, so do check that out. Links can be found in the video description below.
Timing relays are extensively used in industrial applications, HVAC systems, and building services to provide time delay switching. For example, they can start a motor, control an electrical load, or automate an action. They play a vital role in targeted logic needs.
A common example you may have seen is in a corridor or stairwell that is infrequently used, such as in a workplace or apartment block. We don’t want the light to stay on constantly; we want it to automatically turn off. So, once the light switch is pressed, the time delay relay keeps the light on for a certain amount of time, and once this time expires, it will automatically cut the power to the light.
Timing relays can be applied to almost any application. They are available as plug-in devices, base-mounted devices, circuit boards, and even DIN rail-mounted controls. Traditionally, timing relays were available only as single-function, single-time range devices. These devices are still available and are typically used in applications with very simple timing needs. However, we can also find more advanced timing relays with different functions and multiple timing ranges. Most are capable of controlling voltages or currents over a wide range, and no programming language is required to set them up. We simply adjust the settings via the dials, and the manufacturer’s guide will instruct you on how to do this.
The time delay relays and switches will operate automatically once set up and provided with a trigger or a signal to cause the action. With multi-function relays, we often find an LED built into the device that flashes at different intervals to indicate what function is currently being performed. The manufacturer’s guide will tell us what function the LED is indicating.
To apply a time delay relay or switch, we need to consider where the device will be installed, what will trigger the device, how long the delay will be before energizing the secondary side, or how long the secondary side will be energized. Where have you seen timing relays used, or where could you apply one? Let me know your thoughts and ideas in the comments section below.
Sometimes, we need the secondary side of a relay to remain on for a given amount of time. For example, an external radiant heater at a restaurant with outdoor seating. When a customer is cold, they flip the switch. These heaters use a lot of energy, so we don’t want them left on for hours at a time, especially since the customer won’t be there for too long. We can use a timing relay to automatically turn the heater off after a set duration, like 30 minutes.
If we look at a simple circuit with a battery and an LED, when the switch is closed, the LED illuminates. When the switch is opened, the LED instantly turns off. To delay the turning off of the LED, we could place a capacitor in parallel with the LED. This way, when the switch is closed, the LED illuminates, and the capacitor charges. When the switch is opened, the capacitor discharges, and the LED remains illuminated. We can use different size capacitors to change how long the LED remains powered.
We could even use a variable capacitor to allow adjustment of this time period. The switch could be the secondary side of a relay and use an input signal on the primary side to start the timer on the secondary side. Alternatively, the LED could be on the primary side of a solid-state relay, using the LED to provide optical coupling to a phototransistor on the secondary side.
However, the problem we face with this design is that the discharge rate of the capacitor is not linear, so the LED slowly dims until it eventually turns off. To ensure the LED remains on when the switch is opened but also automatically turns off if it becomes too dim, we could add a transistor to the circuit. The transistor will act like a switch.
There are different types of transistors, but we won’t go into detail on those in this video. For now, we will consider that the main circuit is connected across two of the transistor’s three pins. This type of transistor will normally block the flow of current in a circuit, but when a certain voltage is applied to the base pin, the transistor allows the current to flow. When the voltage to the base pin is removed, the transistor stops the flow of current in the main circuit.
This diagram shows a simple delay timing-off circuit using a transistor, capacitor, LED, and switch. The resistors are used to limit the current and protect the components. We can control the current in the main circuit by sending a signal to the base pin of the transistor. This signal is a small voltage. The transistor will only allow current to flow in the main circuit if the voltage at the base pin is at or above a certain level, typically 0.7 volts. If the voltage at the base pin falls below this minimum level, it will not allow current to flow.
With the switch open, the LED does not light up because no voltage is detected at the transistor’s base pin, so the transistor acts like an open switch and prevents current from flowing in the main circuit. With the switch closed, electricity flows to the base pin of the transistor. The transistor detects the voltage and determines that it is above the minimum level, so it allows current to flow in the main circuit, illuminating the LED. Meanwhile, the capacitor charges.
When the switch is opened, the main power supply to the transistor’s base pin is disconnected. The capacitor now begins to discharge and provides the voltage to the base pin. This permits the transistor to keep allowing current through the main circuit, so the LED remains on. When the voltage level of the capacitor falls below the minimum trigger value of the transistor, it will turn off and stop the current from flowing in the main circuit, causing the LED to turn off. The storage capacity of the capacitor determines how long the circuit is powered.
This simple design is for a time delay switch, but we could integrate this into a relay. By the way, we have covered how capacitors work in detail in our previous video, so check that out as well. Links can be found in the video description below.
Sometimes, we need the secondary side of a relay to remain off for a given amount of time. For example, when large inductive loads turn on or off, perhaps from a sudden loss of power or the startup of a large induction motor, large voltage spikes or inrush currents can occur due to the strong magnetic flux in the circuit. These surges can damage components and equipment. If a short delay is provided, such damage can be avoided. Time delay relay circuits are used for this purpose.
If we look at a simple delay time-on circuit, the transistor is preventing the lamp from turning on. The transistor needs a minimum voltage to open and allow the lamp to turn on. When we close the switch, the transistor receives this voltage and instantly allows current to flow. To delay this, we could connect a zener diode to the base pin of the transistor and then connect a resistor and capacitor in parallel between the diode and the switch. Diodes only allow current to flow in one direction and block current flowing in the opposite way. However, if a zener diode is provided a certain reverse voltage, it will open and allow current to flow in the opposite direction, known as the breakdown voltage.
We can use this to control the transistor by only opening when a certain voltage is applied. When we close the switch, the current will slowly charge the capacitor. The zener diode continues to block the current to the transistor, and the lamp remains off as the capacitor charges. The voltage increases until it exceeds the zener diode’s breakdown voltage. At this moment, the diode allows current to flow through it and reach the transistor, which then allows current to flow through it, turning the lamp on.
When we disconnect the switch, the capacitor continues to supply the voltage, keeping the zener diode and transistor open. Current flows through the resistor until it drains the capacitor. Once the voltage of the capacitor falls below the breakdown voltage, the zener diode again blocks the current to the transistor, and the lamp turns off.
Now, when the circuit is energized, the load will not turn on instantly; it will only turn on once the capacitor is charged to exceed the zener diode’s breakdown voltage. This is a fairly simple design, and it’s common to find an IC chip inside something as simple as a 555 timer used instead. However, this simple design gives you a visual understanding of how a circuit might work.
Okay, that’s it for this video! To continue learning about electrical and controls engineering, check out one of the videos on screen now, and I’ll catch you there for the next lesson. Don’t forget to follow us on Facebook, Twitter, LinkedIn, Instagram, and visit TheEngineeringMindset.com.
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This version removes any informal language and maintains a professional tone while retaining the essential information from the original transcript.
Time – The continuous progression of existence and events in the past, present, and future, considered as a whole, often used as a parameter in physics and engineering calculations. – In engineering dynamics, time is a crucial factor in determining the velocity and acceleration of moving objects.
Delay – A period of time by which something is late or postponed, often used in the context of signal processing or system response. – The delay in the feedback loop caused the control system to become unstable.
Relays – Electromechanical switches used to control a circuit by a low-power signal, or where several circuits must be controlled by one signal. – In the electrical engineering lab, students learned how to use relays to automate the switching of high-voltage circuits.
Automation – The use of various control systems for operating equipment with minimal or reduced human intervention. – The automation of the manufacturing process increased efficiency and reduced errors significantly.
HVAC – Heating, Ventilation, and Air Conditioning systems used to regulate the environmental conditions in buildings. – The engineering project focused on designing an energy-efficient HVAC system for the new university campus building.
Circuits – Closed paths through which electric current flows, consisting of various electrical components. – Understanding how circuits work is fundamental for electrical engineering students.
Capacitor – An electrical component used to store and release electrical energy in a circuit. – The capacitor in the circuit was used to smooth out voltage fluctuations.
Voltage – The electrical potential difference between two points in a circuit, driving the flow of current. – Measuring the voltage across the resistor helped determine the current flowing through the circuit.
Control – The process of regulating or directing the operation of a system or device. – The control system was designed to maintain the temperature within the desired range.
Energy – The capacity to do work, which can exist in various forms such as kinetic, potential, thermal, electrical, chemical, and nuclear. – In thermodynamics, energy conservation is a fundamental principle that engineers must consider when designing systems.
