In signal processing , control theory , electronics , and mathematics , overshoot is the occurrence of a signal or function exceeding its target. Undershoot is the same phenomenon in the opposite direction. It arises especially in the step response of bandlimited systems such as low-pass filters . It is often followed by ringing , and at times conflated with the latter.
58-415: The Honeywell T87 Round Thermostat is a thermostat that Honeywell International, Inc. first manufactured in 1953. Henry Dreyfuss designed the thermostat based on a concept by Honeywell engineer Carl Kronmiller . This technology-related article is a stub . You can help Misplaced Pages by expanding it . Thermostat A thermostat is a regulating device component which senses the temperature of
116-508: A baseboard heater or a direct-wired electric furnace. If a line voltage thermostat is used, system power (in the United States, 120 or 240 volts) is directly switched by the thermostat. With switching current often exceeding 40 amperes , using a low voltage thermostat on a line voltage circuit will result at least in the failure of the thermostat and possibly a fire. Line voltage thermostats are sometimes used in other applications, such as
174-598: A physical system and performs actions so that the system's temperature is maintained near a desired setpoint . Thermostats are used in any device or system that heats or cools to a setpoint temperature. Examples include building heating , central heating , air conditioners , HVAC systems, water heaters , as well as kitchen equipment including ovens and refrigerators and medical and scientific incubators . In scientific literature, these devices are often broadly classified as thermostatically controlled loads (TCLs). Thermostatically controlled loads comprise roughly 50% of
232-409: A resistance thermometer (resistance temperature detector). Typically one or more regular batteries must be installed to operate it, although some so-called "power stealing" digital thermostats (operated for energy harvesting ) use the common 24-volt AC circuits as a power source, but will not operate on thermopile powered "millivolt" circuits used in some furnaces. Each has an LCD screen showing
290-421: A bi-metal room thermostat in 1883, and two years later sought a patent for the first multi-zone thermostatic control system. Albert Butz (1849–1905) invented the electric thermostat and patented it in 1886. One of the first industrial uses of the thermostat was in the regulation of the temperature in poultry incubators. Charles Hearson , a British engineer, designed the first modern incubator for eggs, which
348-449: A degree of temperature. Common sensor technologies in use today include: These may then control the heating or cooling apparatus using: Possibly the earliest recorded examples of thermostatic control were built by a Dutch innovator, Cornelis Drebbel (1572–1633), about 1620 in England. He invented a mercury thermostat to regulate the temperature of a chicken incubator . This is one of
406-465: A gas-filled bulb connected to the control unit by a slender copper tube. The bulb is normally located at the top of the oven. The tube ends in a chamber sealed by a diaphragm. As the thermostat heats up, the gas expands applying pressure to the diaphragm which reduces the flow of gas to the burner. A pneumatic thermostat is a thermostat that controls a heating or cooling system via a series of air-filled control tubes. This "control air" system responds to
464-464: A low-power gas valve, which under control of one or more thermostat switches, in turn controls the input of fuel to the burner. This type of device is generally considered obsolete as pilot lights can waste a surprising amount of gas (in the same way a dripping faucet can waste a large amount of water over an extended period), and are also no longer used on stoves, but are still to be found in many gas water heaters and gas fireplaces. Their poor efficiency
522-604: A programmable thermostat which is capable of continuous control (as are at least some Honeywell models), effectively controlling the heater like a lamp dimmer, and gradually increasing and decreasing heating to ensure an extremely constant room temperature (continuous control rather than relying on the averaging effects of hysteresis). Systems which include a fan (electric furnaces, wall heaters, etc.) must typically use simple on/off controls. Newer digital thermostats have no moving parts to measure temperature and instead rely on thermistors or other semiconductor devices such as
580-421: A replacement device. Not shown in the illustration is a separate bimetal thermometer on the outer case to show the actual temperature at the thermostat. As illustrated in the use of the thermostat above, all of the power for the control system is provided by a thermopile which is a combination of many stacked thermocouples, heated by the pilot light. The thermopile produces sufficient electrical power to drive
638-561: A switch to control the HVAC unit. Units with relays will operate millivolt systems, but often make an audible "click" noise when switching on or off. HVAC systems with the ability to modulate their output can be combined with thermostats that have a built-in PID controller to achieve smoother operation. There are also modern thermostats featuring adaptive algorithms to further improve the inertia prone system behaviour. For instance, setting those up so that
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#1732859551473696-416: A temperature change into mechanical displacement, to actuate control of the heating or cooling sources. Electronic thermostats, instead, use a thermistor or other semiconductor sensor, processing temperature change as electronic signals, to control the heating or cooling equipment. Conventional thermostats are example of " bang-bang controllers " as the controlled system either operates at full capacity once
754-421: Is acceptable in water heaters, since most of the energy "wasted" on the pilot still represents a direct heat gain for the water tank. The Millivolt system also makes it unnecessary for a special electrical circuit to be run to the water heater or furnace; these systems are often completely self-sufficient and can run without any external electrical power supply. For tankless "on demand" water heaters, pilot ignition
812-442: Is in general inaccurate, inefficient and high-level mechanical wear, but for components like compressors, it still has a significant cost advantage compared with more advanced ones allowing continuously variable capacity. Another consideration is the time delay of the controlled system. To improve the control performance of the system, thermostats can include an "anticipator", which stops heating/cooling slightly earlier than reaching
870-686: Is not suitable the PID control can also makes sure that the temperature is very stable (for instance, by reducing overshoots by fine tuning PID constants for set value (SV) or maintaining temperature in a band by deploying hysteresis control. ) Most digital thermostats in common residential use in North America and Europe are programmable thermostats , which will typically provide a 30% energy savings if left with their default programs; adjustments to these defaults may increase or reduce energy savings. The programmable thermostat article provides basic information on
928-432: Is preferable because it is faster than hot-surface ignition and more reliable than spark ignition. Some programmable thermostats - those that offer simple "millivolt" or "two-wire" modes - will control these systems. The majority of modern heating/cooling/heat pump thermostats operate on low voltage (typically 24 volts AC ) control circuits. The source of the 24 volt AC power is a control transformer installed as part of
986-422: Is required, a PID or MPC controller is preferred. However, they are nowadays mainly adopted for industrial purposes, for example, for semiconductor manufacturing factories or museums. Early technologies included mercury thermometers with electrodes inserted directly through the glass, so that when a certain (fixed) temperature was reached the contacts would be closed by the mercury. These were accurate to within
1044-402: The convolution with the impulse response , which is a sinc function . The overshoot and undershoot can be understood in this way: kernels are generally normalized to have integral 1, so they send constant functions to constant functions – otherwise they have gain . The value of a convolution at a point is a linear combination of the input signal, with coefficients (weights)
1102-438: The sinc function ; in signal processing terms , this is a low-pass filter . In signal processing , overshoot is when the output of a filter has a higher maximum value than the input, specifically for the step response , and frequently yields the related phenomenon of ringing artifacts . This occurs for instance in using the sinc filter as an ideal ( brick-wall ) low-pass filter . The step response can be interpreted as
1160-404: The air temperature using the differential expansion of two metals to actuate an on/off switch. Typically the central system would be switched on when the temperature drops below the setpoint on the thermostat, and switched off when it rises above, with a few degrees of hysteresis to prevent excessive switching. Bi-metallic sensing is now being superseded by electronic sensors . A principal use of
1218-518: The anticipation function. In some electronic thermostats, the thermistor anticipator may be located outdoors, providing a variable anticipation depending on the outdoor temperature. Thermostat enhancements include outdoor temperature display, programmability, and system fault indication. While such 24 volt thermostats are incapable of operating a furnace when the mains power fails, most such furnaces require mains power for heated air fans (and often also hot-surface or electronic spark ignition) rendering moot
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#17328595514731276-402: The approximation of functions, overshoot is one term describing quality of approximation. When a function such as a square wave is represented by a summation of terms, for example, a Fourier series or an expansion in orthogonal polynomials , the approximation of the function by a truncated number of terms in the series can exhibit overshoot, undershoot and ringing . The more terms retained in
1334-504: The bi-metallic thermostat today is in individual electric convection heaters, where control is on/off, based on the local air temperature and the setpoint desired by the user. These are also used on air-conditioners, where local control is required. This follows the same nomenclature as described in Relay § Terminology and Switch § Contact terminology . A thermostat is considered to be activated by thermal energy, thus “normal” refers to
1392-477: The building), the thermostat will cause small electric motors to open valves or dampers and start the furnace or boiler if it is not already running. Most programmable thermostats will control these systems. Depending on what is being controlled, a forced-air air conditioning thermostat generally has an external switch for heat/off/cool, and another on/auto to turn the blower fan on constantly or only when heating and cooling are running. Four wires come to
1450-412: The centrally-located thermostat from the main heating/cooling unit (usually located in a closet , basement , or occasionally in the attic ): One wire, usually red, supplies 24 volts AC power to the thermostat, while the other three supply control signals from the thermostat, usually white for heat, yellow for cooling, and green to turn on the blower fan. The power is supplied by a transformer , and when
1508-402: The control of fan-coil (fan powered from line voltage blowing through a coil of tubing which is either heated or cooled by a larger system) units in large systems using centralized boilers and chillers , or to control circulation pumps in hydronic heating applications. Some programmable thermostats are available to control line-voltage systems. Baseboard heaters will especially benefit from
1566-408: The current temperature, and the current setting. Most also have a clock , and time-of-day and even day-of-week settings for the temperature, used for comfort and energy conservation . Some advanced models have touch screens , or the ability to work with home automation or building automation systems. Digital thermostats use either a relay or a semiconductor device such as triac to act as
1624-412: The definition of overshoot in an electronics context . For second-order systems, the percentage overshoot is a function of the damping ratio ζ and is given by The damping ratio can also be found by In electronics, overshoot refers to the transitory values of any parameter that exceeds its final (steady state) value during its transition from one value to another. An important application of
1682-413: The engine near its optimum operating temperature by regulating the flow of coolant to an air-cooled radiator . This type of thermostat operates using a sealed chamber containing a wax pellet that melts and expands at a set temperature. The expansion of the chamber operates a rod which opens a valve when the operating temperature is exceeded. The operating temperature is determined by the composition of
1740-471: The first recorded feedback-controlled devices. Modern thermostatic control was developed in the 1830s by Andrew Ure (1778–1857), a Scottish chemist. The textile mills of the time needed a constant and steady temperature to operate optimally, so Ure designed the bimetallic thermostat, which would bend as one of the metals expanded in response to the increased temperature and cut off the energy supply. Warren S. Johnson (1847–1911), of Wisconsin , patented
1798-681: The flow of a heat transfer fluid as needed, to maintain the correct temperature. A thermostat can often be the main control unit for a heating or cooling system, in applications ranging from ambient air control to automotive coolant control. Thermostats are used in any device or system that heats or cools to a setpoint temperature. Examples include building heating , central heating , and air conditioners , kitchen equipment such as ovens and refrigerators , and medical and scientific incubators . Thermostats use different types of sensors to measure temperatures and actuate control operations. Mechanical thermostats commonly use bimetallic strips , converting
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1856-578: The functionality of the thermostat. In other circumstances such as piloted wall and "gravity" (fanless) floor and central heaters the low voltage system described previously may be capable of remaining functional when electrical power is unavailable. There are no standards for wiring color codes, but convention has settled on the following terminal codes and colors. In all cases, the manufacturer's instructions should be considered definitive. Older, mostly deprecated designations: Line voltage thermostats are most commonly used for electric space heaters such as
1914-417: The heater core. The passenger side tank of the radiator is used as a bypass to the thermostat, flowing through the heater core. This prevents formation of steam pockets before the thermostat opens, and allows the heater to function before the thermostat opens. Another benefit is that there is still some flow through the radiator if the thermostat fails. A thermostatic mixing valve uses a wax pellet to control
1972-406: The heating/cooling equipment. The advantage of the low voltage control system is the ability to operate multiple electromechanical switching devices such as relays , contactors, and sequencers using inherently safe voltage and current levels. Built into the thermostat is a provision for enhanced temperature control using anticipation. A heat anticipator generates a small amount of additional heat to
2030-479: The heating/cooling system is off, it would be wise to keep the thermostat set to "cool", despite what the temperature is outside. On the other hand, if the temperature of the controlled area falls below the desired degree, then it is advisable to turn the thermostat to "heat". Overshoot (signal) Maximum overshoot is defined in Katsuhiko Ogata's Discrete-time control systems as "the maximum peak value of
2088-408: The individual flow. However, thermostatic radiator valves (TRV) are now being widely used. Purely mechanical thermostats are used to regulate dampers in some rooftop turbine vents, reducing building heat loss in cool or cold periods. Some automobile passenger heating systems have a thermostatically controlled valve to regulate the water flow and temperature to an adjustable level. In older vehicles
2146-570: The mixing of hot and cold water. A common application is to permit operation of an electric water heater at a temperature hot enough to kill Legionella bacteria (above 60 °C, 140 °F), while the output of the valve produces water that is cool enough to not immediately scald (49 °C, 120 °F). A wax pellet driven valve can be analyzed through graphing the wax pellet's hysteresis which consists of two thermal expansion curves; extension (motion) vs. temperature increase, and contraction (motion) vs. temperature decrease. The spread between
2204-409: The operation, selection and installation of such a thermostat. With non-zoned (typical residential, one thermostat for the whole house) systems, when the thermostat's R (or Rh) and W terminals are connected, the furnace will go through its start-up procedure and produce heat. With zoned systems (some residential, many commercial systems — several thermostats controlling different "zones" in
2262-599: The overall electricity demand in the United States. A thermostat operates as a "closed loop" control device, as it seeks to reduce the error between the desired and measured temperatures. Sometimes a thermostat combines both the sensing and control action elements of a controlled system, such as in an automotive thermostat. The word thermostat is derived from the Greek words θερμός thermos , "hot" and στατός statos , "standing, stationary". A thermostat exerts control by switching heating or cooling devices on or off, or by regulating
2320-473: The pressure changes (due to temperature) in the control tube to activate heating or cooling when required. The control air typically is maintained on "mains" at 15-18 psi (although usually operable up to 20 psi). Pneumatic thermostats typically provide output/ branch/ post-restrictor (for single-pipe operation) pressures of 3-15 psi which is piped to the end device (valve/ damper actuator/ pneumatic-electric switch, etc.). The pneumatic thermostat
2378-402: The response curve measured from the desired response of the system." In control theory , overshoot refers to an output exceeding its final, steady-state value. For a step input , the percentage overshoot (PO) is the maximum value minus the step value divided by the step value. In the case of the unit step, the overshoot is just the maximum value of the step response minus one. Also see
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2436-415: The sensing element while the cooling appliance is not operating. This causes the contacts to energize the cooling equipment slightly early, preventing the space temperature from climbing excessively. Cooling anticipators are generally non-adjustable. Electromechanical thermostats use resistance elements as anticipators. Most electronic thermostats use either thermistor devices or integrated logic elements for
2494-418: The sensing element while the heating appliance is operating. This opens the heating contacts slightly early to prevent the space temperature from greatly overshooting the thermostat setting. A mechanical heat anticipator is generally adjustable and should be set to the current flowing in the heating control circuit when the system is operating. A cooling anticipator generates a small amount of additional heat to
2552-526: The series, the less pronounced the departure of the approximation from the function it represents. However, though the period of the oscillations decreases, their amplitude does not; this is known as the Gibbs phenomenon . For the Fourier transform , this can be modeled by approximating a step function by the integral up to a certain frequency, which yields the sine integral . This can be interpreted as convolution with
2610-414: The setpoint is reached, or keeps completely off. Although it is the simplest program to implement, such control method requires to include some hysteresis in order to prevent excessively rapid cycling of the equipment around the setpoint. As a consequence, conventional thermostats cannot control temperatures very precisely. Instead, there are oscillations of a certain magnitude, usually 1-2 °C. Such control
2668-495: The setpoint, as the system will continue to produce heat for a short while. Turning off exactly at the setpoint will cause actual temperature to exceed the desired range, known as " overshoot ". Bimetallic sensors can include a physical "anticipator", which has a thin wire touched on the thermostat. When current passes the wire, a small amount of heat is generated and transferred to the bimetallic coil. Electronic thermostats have an electronic equivalent. When higher control precision
2726-428: The sinc function, then the value of the filtered signal will instead be an affine combination of the input values, and may fall outside of the minimum and maximum of the input signal, resulting in undershoot and overshoot. Overshoot is often undesirable, particularly if it causes clipping , but is sometimes desirable in image sharpening, due to increasing acutance (perceived sharpness). A closely related phenomenon
2784-663: The state in which temperature is below the setpoint. Any leading number stands for number of contact sets, like "1NO", "1NC" for one contact set with two terminals. "1CO" will also have one contact set, even if it is a switch-over with three terminals. The illustration is the interior of a common two wire heat-only household thermostat, used to regulate a gas -fired heater via an electric gas valve. Similar mechanisms may also be used to control oil furnaces, boilers, boiler zone valves , electric attic fans, electric furnaces, electric baseboard heaters, and household appliances such as refrigerators, coffee pots and hair dryers. The power through
2842-438: The temperature in the morning at 7 a.m. should be 21 °C (69.8 °F), makes sure that at that time the temperature will be 21 °C (69.8 °F), where a conventional thermostat would just start working at that time. The algorithms decide at what time the system should be activated in order to reach the desired temperature at the desired time. Other thermostat used for process/industrial control where on/off control
2900-408: The term is to the output signal of an amplifier. Usage : Overshoot occurs when the transitory values exceed final value. When they are lower than the final value, the phenomenon is called "undershoot" . A circuit is designed to minimize rise time while containing distortion of the signal within acceptable limits. Also see the definition of overshoot in a control theory context . In
2958-424: The thermostat controls the application of engine vacuum to actuators that control water valves and flappers to direct the flow of air. In modern vehicles, the vacuum actuators may be operated by small solenoids under the control of a central computer. Perhaps the most common example of purely mechanical thermostat technology in use today is the internal combustion engine cooling system thermostat, used to maintain
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#17328595514733016-431: The thermostat is provided by the heating device and may range from millivolts to 240 volts in common North American construction, and is used to control the heating system either directly (electric baseboard heaters and some electric furnaces) or indirectly (all gas, oil and forced hot water systems). Due to the variety of possible voltages and currents available at the thermostat, caution must be taken when selecting
3074-423: The thermostat makes contact between the 24 volt power and one or two of the other wires, a relay back at the heating/cooling unit activates the corresponding heat/fan/cool function of the unit(s). A thermostat, when set to "cool", will only turn on when the ambient temperature of the surrounding room is above the set temperature. Thus, if the controlled space has a temperature normally above the desired setting when
3132-614: The up and down curves visually illustrate the valve's hysteresis; there is always hysteresis within wax driven valves due to the phase transition or phase change between solids and liquids. Hysteresis can be controlled with specialized blended mixes of hydrocarbons; tight hysteresis is what most desire, however some applications require broader ranges. Wax pellet driven valves are used in anti scald, freeze protection, over-temp purge, solar thermal energy or solar thermal , automotive, and aerospace applications among many others. Thermostats are sometimes used to regulate gas ovens. It consists of
3190-439: The values of the kernel. If a kernel is non-negative, such as for a Gaussian kernel , then the value of the filtered signal will be a convex combination of the input values (the coefficients (the kernel) integrate to 1, and are non-negative), and will thus fall between the minimum and maximum of the input signal – it will not undershoot or overshoot. If, on the other hand, the kernel assumes negative values, such as
3248-424: The wax. Once the operating temperature is reached, the thermostat progressively increases or decreases its opening in response to temperature changes, dynamically balancing the coolant recirculation flow and coolant flow to the radiator to maintain the engine temperature in the optimum range. On many automobile engines, including all Chrysler Group and General Motors products, the thermostat does not restrict flow to
3306-471: Was invented by Warren Johnson in 1895 soon after he invented the electric thermostat. In 2009, Harry Sim was awarded a patent for a pneumatic-to-digital interface that allows pneumatically controlled buildings to be integrated with building automation systems to provide similar benefits as direct digital control (DDC). Water and steam based central heating systems have traditionally had overall control by wall-mounted bi-metallic strip thermostats. These sense
3364-424: Was taken up for use on poultry farms in 1879. This covers only devices which both sense and control using purely mechanical means. Domestic water and steam based central heating systems have traditionally been controlled by bi-metallic strip thermostats, and this is dealt with later in this article. Purely mechanical control has been localised steam or hot-water radiator bi-metallic thermostats which regulated
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