Into To Control Systems (140104a) Flashcards
Actual spring range
The change in the applied signal that operated the controlled device while under actual conditions. In addition to the normal spring range, an actual spring range must overcome forced such as fluid flow and friction.
Ambient temperature
Temperature of the surrounding environment.
Amplifier
A device that receives an input input signal from an independent source and delivers an output signal that is related to and generally greater than the input signal.
Analog
A control action that is continuously variable. A damper must move from closed to open through all intermediary positions, rather than being instantly open.
Anticipating control
In order to produce a smaller differential of the controlled property, artificial means activate this type of control earlier than it would otherwise activate. Heat and cool anticipators are common in thermostats
Aquastat
A thermostat that controls water temperature.
Averaging element
A thermostat sensing element that responds to the average duct temperatures.
Bimetal element
A metal element that forms from two metals that have different coefficients of thermal expansion. In this element you find temperature indicating and controlling devices, among others.
Bulb
A remote thermostat sensing element that responds to the temperature in the immediate vicinity of the bulb.
Capillary tube
A tube with a small internal diameter that functions as a liquid refrigerant flow control or expansion device between high and low sides. A capillary tube also transmitted pressure from the sensing bulb of some temperature controls of the operating element.
Closed-loop system
The arrangement of components ( such as a heating unit, valve and thermostat) where each component affects the others and can react accordingly in order to allow system feedback.
Coefficient of linear thermal expansion
The change in length of a substance per degree change in temperature at a constant pressure (linear expansivity)
Control agent
The energy that the control system manipulates to cause a change in the controlled medium
Control point
The actual valve of the controlled variable that the controller maintains at any given time. That is, the actual temperature that you measure in the space (such as a room)
Control system
The configuration of equipment that permits the management of a variable.
Controlled device
The instrument that receives the controller’s output signal and regulates the flow of the control agent.
Controlled medium
The substance (usually air, water or steam) who’s characteristics (such as temperature, pressure, flow rate, volume and concentration) the addition or removal of energy varies
Controlled variable
The quantity or condition of the controlled medium that the main controller, such as a thermostat, measures and controls.
Controller
A device that senses and measures changes in the controlled variable. As a result, it meters energy in a usable form (output signal) that holds the controlled variable within predetermined limits
Controller feedback
The signal that represents a change in a measured variable, which a sensor transmits back to a controller for evaluation. Feedback signals are either analog or digital. Changes between the controlled variable and the setpoint initiate corrective actions.
Corrective action
A control operation that results from a deviation in a measured variable
Cycle
One complete revolution or execution through a repeatable process.
Damper
A movable plate with a vessel or chamber that starts, stops, or varies the volume of air entering, leaving, or passing through that vessel or chamber.
Damper linkage
Linkage that connects the motor to the damper. It usually consists of a push rod, two crank arms and two ball joints.
Damper, opposed blade.
A multiple blade damper with opposed blades. Each alternating blade rotates in a direction opposite to that of the ones beside it.
Damper, parallel blade
All blades rotate in the same direction. The effect provides linear airflow characteristic. The flow is nearly proportional to damper shaft rotation.
**Deviation**
The difference between the setpoint and the value of the controlled variable at any instant.
**Differential**
The difference in the values of the controlled variable that will activate a two-position controller to change an output of either maximum of zero to the opposite extreme with no immediate steps
Digital (Binary)
A method of communicating in an electronic control system where the signal is a series of ones and zeros or high or low signals that identify a condition. Digital signals may be a serial (RS232) or parallel (printer point)
Direct acting
The output signal changes in the same direction that the controlled or measured variable changes; that is; an increase in the controlled or measured variable results in an increased output signal.
Economizer control
A system of ventilation control that controls outdoor and return air dampers in order to maintain the proper mixed-air temperature for the most economical operation. The system uses outdoor air for free cooling when the outdoor air temperature is below the desired room air temperature.
Equal percentage characteristic
A valve characteristic that matches the percentage of valve openers to the percentage of maximum fluid flow. If the valve is 100% open with the flow rate and 10L per second, when the value moves to 50% open the flow rate changes to 5L per second (50% of the maximum flow rate)
Face-and-bypass damper system (3 of 5)
A heating system that divides the mixed airflow into two duct sections; one through the coil (face) and the other around it he coil (bypass).
High-limit control (Normally Closed)
A device that normally monitors the conditions of the controlled medium and interrupts system operation if the monitored condition becomes excessive.
Humidistat
A regulatory device that changes in humidity actuate. Humidistats control the relative humidity in a space, automatically.
Input
- ) The point At which you enter data
2. ) To enter data
Invar
A metal alloy that consists of nickel and iron. Controls that require a metal with a low coefficient or thermal expansion.
Lag (2 points)
- ) A delay in the effect of a changed condition at one point in a system or in effect of some other related condition.
- ) The delay in the action of a control’s sensing element that results from the time the sensing element takes to reach equilibrium with the controlled property (such as temperature and flow lag)
Limit (Safety device)
2 points
- ) A switch (such as In a motor) that cuts off power to the damper motor windings when it is in its full open position.
- ) a device that monitors the condition of the controlled medium.
Measured variable
The Uncontrolled variable (such as temperature, relative humidity or pressure) that the measuring element senses.
Measuring element
- ) in a control system with a pneumatic controller, it is that part of the controller that measures a change in temperature, humidity or pressure.
- ) in a control system with an electronic controller, it is that part of the controller that Measures a change in the temperature, humidity or pressure. The result is a change in resistance that varies a current flow.
Manipulated Variable
A quantity or condition that the automatic control system regulates in a matter that causes the desired change in the __________. The ________ is a characteristic of the control agent.
Modulating
Any controlled movement that changes through tiny increments and deferments, as compared to a simple two position control movement with two large movements.
Modulating control
A mode of automatic control in which the auction of the final control element of proportional to the deviation from the setpoint of the co trolled medium.
Modulating Motor
An electric motor that drives a controlled device, such as a damper. It can position controlled device mechanisms anywhere between fully opened and fully closed in proportion to the deviation of the controlled medium.
Normally Closed. (NC)
The position of a switching device at rest with its switch contractors connected. This allows electrical current or fluid flow to continue as long as the switching mechanism is not activated.
Normally Open (NO)
The position of a switching device at rest with no switch contacts connected. This does not allow electrical current or fluid to flow as long as the switching mechanism is not activated.
Offset
- ) a sustained deviation between the actual control point and the setpoint under stable operating conditions
- ) The difference between the setpoint of the controller and the control point of the controlled variable.
Open-loop system
An arrangement of components that does not allow system feedback (does not allow communication)
Primary element
The portion of the controller that first uses energy from the controlled medium to produce a condition that represents the value of the controlled variable.
Process plant
The element of a control system through which energy transfers between the control agent and the controlled medium. It usually effects a change in the controlled variable.
Reset
The process of automatically adjusting the setpoint of a given controller to Compensate for changes in an alternate but associated condition.
Sensing element
The system element or controller component that responds quantitively to the controlled variable and performs the initial measurement operation
Sensitivity
The output change or controller per-unit change in controlled variable
Sequencer
A mechanical or electrical device that the operator sets to initiate a series of events and that forces the events to follow in sequence
Setpoint
The point at which the operator sets the controller. It is the desired controlled variable value that either integral or remote adjustment of the controller can Obtain.
Span
The difference between two limits, usually expressed as a single value with a single unit (such as psi, *F or meters)
Thermocouple
A device for measuring temperature that takes advantage of the fact that, whenever two junctions of two dissimilar metals in an electric circuit are at different temperatures, they generate an electromotive force
Thermistor
A heat sensitive resistor with a resistance change based on temperature changes.
Thermostat
An instrument that responds to changes in temperature and directly or indirectly control temperature. Aka temperature controller
