11-04-2012, 04:06 PM
Design of Automatic Cooling Fan
[attachment=19934]
Comparators
Besides being used as amplifiers, filters and oscillators op-amps are also used as comparators, detectors, limiters, etc. A comparator, as its name implies, compares a signal voltage on one input with a known voltage called the reference voltage on the other input. In its simplest form, it is nothing more than an open-loop op-amp with two analog inputs and a digital output; the output may be (+) or (-) saturation voltage, depending on which input is larger. Comparators are used in circuits such as digital interfacing, Schmitt triggers, discriminators, voltage level detectors and oscillators.
Relays
In designing the “Auto-Fan, for automatic temperature control” we have come across the relay that happens to be the most important part of our circuit. Here we discuss about relays in general but to be more specific the FGR (or the force guided relay) otherwise better known as the electro-magneto mechanical relay.
The FGR
Force guidance in a relay means that the contacts in a contact set must be mechanically linked together so that it is impossible for the NO (Normally Open) Make contacts and the NC (Normally Closed) Break contacts to be closed at the same time. There must be a 0.5mm minimum air gap between open contacts for the entire service life of the relay, even in the case of a failure. The force guidance of the relay contacts must always be preserved even in the event of any malfunction.
Applications
The safest way to turn off a power driven machine to protect human life, the environment or expensive materials is to employ safety-evaluating devices, which use force guided relays. Relays contain many parts that are subject to dynamic, electrical or thermal wear. In order to assure safe function, especially in the case of a failure, appropriate controls are built into the circuits of safety devices.
For instance, one force guided relay can be used to check the condition of another force guided relay or a number of them. If they are in the proper state, they energize and turn off the first relay- this provides the fail-safe or redundant feature necessary for safe operation of any machinery. The force-guided relay is the one component in a safety circuit that enables that circuit to provide redundant and fail-safe operation.
Pre-Cautions
When SCR's are used to operate relays with half-wave rectified power source to make release easy, almost all operations and releases could occur at the same point in the waveform. In the case of heavy loads such as heater loads of temperature controllers, the opening and closing of contacts can occur at any point in the waveform of the control.
Thus, contact life can vary greatly. A thorough check of the controlled equipment should be made to determine true operation condition.
Solid State Relay
Nowadays the SSRs (Solid State Relay) are being used as an alternative for various other kinds of relays. The main reasons being
Long Life Expectancy
Solid-state relays use electronic instead of mechanical devices for load switching while providing a life cycle expectancy of approximately 100,000 energized hours or 11.4 years. This reduces product replacement and downtime.
Low Maintenance
There are no moving parts or contacts to wear out or be affected by vibration and shock. Maintenance cost, parts replacement, and downtime are reduced drastically, if not eliminated altogether.
Reduced Power Costs
The solid-state relay typically requires 25 times less power than electromechanical relays and also generates less heat. This means the panel can typically be smaller, reducing panel space requirements.
CONCLUSION
Design of Automatic Cooling Fan Applications
Automatic Cooling Fan in short Auto-Fan can be successfully used in variety of electronic equipments and gadgets. The reason behind its wide range of application is that the fan is fully automatized, the fan goes to on or off state depending on temperature variations.
It is a known fact that all electronic components and IC’s are all temperature sensitive. Thus to nullify the temperature effect so as to prevent thermal runaways in transistors, we have to use Auto-Fan as it works as a means of heat dissipation. Sometimes due to IC’s being extremely hot, that is if it is used for long hours, or it might happen that some inexperienced person may connect the pin of IC to a higher voltage power supply, then in that case excessive current will flow in a fraction of a second and the IC will burn out if there is no mechanism of controlling heat flow. Sometimes heat sink are used, but Auto-Fan has more advantage than heat sink as it requires circuitry of very small size and it has a small sized highly sensitive thermistor which makes its operation more efficient.
[attachment=19934]
Comparators
Besides being used as amplifiers, filters and oscillators op-amps are also used as comparators, detectors, limiters, etc. A comparator, as its name implies, compares a signal voltage on one input with a known voltage called the reference voltage on the other input. In its simplest form, it is nothing more than an open-loop op-amp with two analog inputs and a digital output; the output may be (+) or (-) saturation voltage, depending on which input is larger. Comparators are used in circuits such as digital interfacing, Schmitt triggers, discriminators, voltage level detectors and oscillators.
Relays
In designing the “Auto-Fan, for automatic temperature control” we have come across the relay that happens to be the most important part of our circuit. Here we discuss about relays in general but to be more specific the FGR (or the force guided relay) otherwise better known as the electro-magneto mechanical relay.
The FGR
Force guidance in a relay means that the contacts in a contact set must be mechanically linked together so that it is impossible for the NO (Normally Open) Make contacts and the NC (Normally Closed) Break contacts to be closed at the same time. There must be a 0.5mm minimum air gap between open contacts for the entire service life of the relay, even in the case of a failure. The force guidance of the relay contacts must always be preserved even in the event of any malfunction.
Applications
The safest way to turn off a power driven machine to protect human life, the environment or expensive materials is to employ safety-evaluating devices, which use force guided relays. Relays contain many parts that are subject to dynamic, electrical or thermal wear. In order to assure safe function, especially in the case of a failure, appropriate controls are built into the circuits of safety devices.
For instance, one force guided relay can be used to check the condition of another force guided relay or a number of them. If they are in the proper state, they energize and turn off the first relay- this provides the fail-safe or redundant feature necessary for safe operation of any machinery. The force-guided relay is the one component in a safety circuit that enables that circuit to provide redundant and fail-safe operation.
Pre-Cautions
When SCR's are used to operate relays with half-wave rectified power source to make release easy, almost all operations and releases could occur at the same point in the waveform. In the case of heavy loads such as heater loads of temperature controllers, the opening and closing of contacts can occur at any point in the waveform of the control.
Thus, contact life can vary greatly. A thorough check of the controlled equipment should be made to determine true operation condition.
Solid State Relay
Nowadays the SSRs (Solid State Relay) are being used as an alternative for various other kinds of relays. The main reasons being
Long Life Expectancy
Solid-state relays use electronic instead of mechanical devices for load switching while providing a life cycle expectancy of approximately 100,000 energized hours or 11.4 years. This reduces product replacement and downtime.
Low Maintenance
There are no moving parts or contacts to wear out or be affected by vibration and shock. Maintenance cost, parts replacement, and downtime are reduced drastically, if not eliminated altogether.
Reduced Power Costs
The solid-state relay typically requires 25 times less power than electromechanical relays and also generates less heat. This means the panel can typically be smaller, reducing panel space requirements.
CONCLUSION
Design of Automatic Cooling Fan Applications
Automatic Cooling Fan in short Auto-Fan can be successfully used in variety of electronic equipments and gadgets. The reason behind its wide range of application is that the fan is fully automatized, the fan goes to on or off state depending on temperature variations.
It is a known fact that all electronic components and IC’s are all temperature sensitive. Thus to nullify the temperature effect so as to prevent thermal runaways in transistors, we have to use Auto-Fan as it works as a means of heat dissipation. Sometimes due to IC’s being extremely hot, that is if it is used for long hours, or it might happen that some inexperienced person may connect the pin of IC to a higher voltage power supply, then in that case excessive current will flow in a fraction of a second and the IC will burn out if there is no mechanism of controlling heat flow. Sometimes heat sink are used, but Auto-Fan has more advantage than heat sink as it requires circuitry of very small size and it has a small sized highly sensitive thermistor which makes its operation more efficient.