Deadband
Encyclopedia
A deadband is an area of a signal range
or band where no action occurs (the system is dead). Deadband is used in voltage regulator
s and other controllers. The purpose is common, to prevent oscillation
or repeated activation-deactivation cycle
s (called 'hunting' in proportional control
systems).
that keep the voltage
within certain predetermined limits, but there is a range of voltage in-between during which no changes are made, such as, maybe, between 112 to 118 volts (deadband is 6 volts here), or 215 to 225 volts (deadband is 10 volts here).
. With hysteresis there is no dead zone, the output is always in one direction or another. Devices with hysteresis have memory, in that previous system states dictate future states; in contrast. Examples of devices with hysteresis are thermostats and smoke alarms.
exhibit hysteresis. The furnace in the basement of a house is adjusted automatically by the thermostat to be switched on as soon as the temperature at the thermostat falls to 18 °C, for example, and the furnace is switched off by the thermostat as soon as the temperature at the thermostat reaches 22 °C. There is no temperature at which the house is not being heated or allowed to cool (furnace on or off).
as soon as the level of smoke reaches a certain starting value, x, then the smoke detector stays in the alarm position until the level of smoke has been reduced to level y, after which the smoke detector is reset automatically to "normal". The hysteresis here is x minus y.
Range
-In mathematics:* Range , the set of all output values produced by a function* Interval , also called a range, a set of real numbers that includes all numbers between any two numbers in the set...
or band where no action occurs (the system is dead). Deadband is used in voltage regulator
Voltage regulator
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may use an electromechanical mechanism, or electronic components...
s and other controllers. The purpose is common, to prevent oscillation
Oscillation
Oscillation is the repetitive variation, typically in time, of some measure about a central value or between two or more different states. Familiar examples include a swinging pendulum and AC power. The term vibration is sometimes used more narrowly to mean a mechanical oscillation but sometimes...
or repeated activation-deactivation cycle
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
s (called 'hunting' in proportional control
Proportional control
A proportional control system is a type of linear feedback control system. Two classic mechanical examples are the toilet bowl float proportioning valve and the fly-ball governor....
systems).
Voltage regulators
In some substations there are regulatorsVoltage regulator
A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level. A voltage regulator may be a simple "feed-forward" design or may include negative feedback control loops. It may use an electromechanical mechanism, or electronic components...
that keep the voltage
Voltage
Voltage, otherwise known as electrical potential difference or electric tension is the difference in electric potential between two points — or the difference in electric potential energy per unit charge between two points...
within certain predetermined limits, but there is a range of voltage in-between during which no changes are made, such as, maybe, between 112 to 118 volts (deadband is 6 volts here), or 215 to 225 volts (deadband is 10 volts here).
Backlash
Gear teeth with slop (backlash) exhibit deadband. There is no drive from the input to the output shaft in either direction while the teeth are not meshed.Hysteresis is not deadband
Deadband is different from hysteresisHysteresis
Hysteresis is the dependence of a system not just on its current environment but also on its past. This dependence arises because the system can be in more than one internal state. To predict its future evolution, either its internal state or its history must be known. If a given input alternately...
. With hysteresis there is no dead zone, the output is always in one direction or another. Devices with hysteresis have memory, in that previous system states dictate future states; in contrast. Examples of devices with hysteresis are thermostats and smoke alarms.
Thermostats
ThermostatsThermostat
A thermostat is the component of a control system which regulates the temperature of a system so that the system's temperature is maintained near a desired setpoint temperature. The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer...
exhibit hysteresis. The furnace in the basement of a house is adjusted automatically by the thermostat to be switched on as soon as the temperature at the thermostat falls to 18 °C, for example, and the furnace is switched off by the thermostat as soon as the temperature at the thermostat reaches 22 °C. There is no temperature at which the house is not being heated or allowed to cool (furnace on or off).
Alarms
A smoke detector is also an example of hysteresis, not deadband. The smoke detector at the ceiling of the kitchen starts the alarmAlarm
An alarm device or system of alarm devices gives an audible or visual alarm signal about a problem or condition.Alarm devices include:* burglar alarms, designed to warn of burglaries; this is often a silent alarm: the police or guards are warned without indication to the burglar, which increases...
as soon as the level of smoke reaches a certain starting value, x, then the smoke detector stays in the alarm position until the level of smoke has been reduced to level y, after which the smoke detector is reset automatically to "normal". The hysteresis here is x minus y.