Glossary of Terms: A

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A to D or A/D Converter
Analog to Digital. This electronic hardware converts an analog signal like voltage, electric current, temperature, or pressure into a digital number that a computer can process and interpret.
Absolute Pressure
Sum of gauge pressure plus atmospheric pressure. Zero only in a perfect vacuum.
Absolute Pressure Sensor
A sensor that measures input pressure in relation to zero pressure (a total vacuum on one side of the diaphragm).
AC line frequency
The frequency of the alternating current power line measured in Hertz (Hz), usually 50 or 60Hz.
Rate of change of velocity. Acceleration has two characteristics: magnitude and direction.
Access Point
The hub of a wireless network. Also called a wireless router, wireless gateway, or base station. Wireless clients connect to it, and traffic between clients must travel through it.
Degree of conformity of an indicated value to an accepted standard value or ideal value. The various errors (such as linearity, hysteresis, repeatability and temperature shift) attributing to the accuracy of a device are usually expressed as a percent of full scale output (Span)
Accuracy - Calibration Accuracy
Closeness between the value indicated by a measuring instrument and a physical constant or known standard.
Accuracy - Control Accuracy
The ability to maintain a process at the desired setting. This is a function of the entire system, including sensors, controllers, heaters, loads, and inefficiencies.
Accuracy - Indication Accuracy
Closeness between the displayed value and a measured value. Usually expressed as a + or -, a percent of span or number of digits.
Accuracy - Setting Accuracy
Closeness between the value established by an input device, such as a dial, and the desired value. Usually expressed as a percent of span or number of digits.
The response of an output when the process variable is changed. See also direct action, reverse action.
Activating force
Depending on the My-Com type an activating force in the range of 30 cN to 100 cN is required to open the switch. Special versions may require up to 250 cN.
Active area
The active area of a through beam sensor is equivalent to the lens size of the emitter or receiver. The acceptance cone is larger. This is important when considering alignment and operation near shiny surfaces.
Actual sensing range Tb
The actual sensing range Tb is between the adjusted nominal sensing distance Tw and the blind region. The blind region is the area immediately before the lens, in which target recognition cannot be guaranteed. Within the actual sensing range, a standard Kodak white target will always be detected.
The present value of the controlled variable.
Actuation Signal
Setpoint minus controlled variable at a given instant.
Controlled motor, relay, or solenoid in which electric energy is converted into a rotary, linear, or switching action. Actuators can affect a change in controlled variable by operating final control elements a number of times.
Actuator MDBA
Simple and cost-effective. For simple and cost-effective format change with an already existing external control which works without fieldbus.
Actuator MSAA
Compact and decentralized The actuator MSAA is equipped with an absolute position encoder. Therefore, time-consuming reference runs are not necessary.
Actuator Tip
The actuator tip of a standard My-Com is made of zirconium oxyde ZrO2. Hard metal or ruby is used for a selected number of special types.
A numerical identifier for a controller when used in computer communications.
Adjustable (Sn)
The sensing distance of the sensor may be adjusted by means of a potentiometer. See also potentiometer.
Adjustment Aid
The LED indicates the intensity of the signal which has been reflected by the object, as well as the switching state of the output.
LED on: The object is reliably detected with a signal strength reserve of 50%. The output is switched.
LED off: No target detected, output is not switched
LED flashing: Unreliable detection of the target. The output is activated / switched.
Air Stream
The narrow sonic beam angle may be affected by strong air streams in excess of 10 m/second.
Audible device or visible signal indicating a malfunction or off-normal condition.
Alarm Circuit
Electrical circuit that includes bell, horn, or similar device to signal unsafe condition.
Alarm - Deviation Alarm
Warns that a process has exceeded or fallen below a certain range around the set point. Alarms can be referenced at a fixed number of degrees, plus or minus, from a set point.
Alarm - Loop Alarm
Any alarm system that includes high and low process deviation band, dead band, digital inputs, and auxiliary control outputs.
Alarm - Process Alarm
Warns that process values exceed the process alarm setting. A fixed value independent of set point.
Alternating Current
Electrical current that reverses its direction of flow at regular intervals and has alternately positive and negative values.
In the area. (1) light: Light in the area of the photosensor, but not originating with the control light source. Ambient light can adversely affect non-modulated control operation, and should be screened, if possible, from the sensor; 2) Temperature: Average temperature of surrounding medium such as water, air, or earth, into which the heat of the equipment is dissipated.
Ambient Conditions
Conditions measured in the immediate area. The term implies that the measurement is only accurate for the specific location it was taken. This term can be applied to any unit of measure, such as temperature, pressure, humidity, light intensity, etc.
Ambient Light
Ambient light refers to any outside light such as sunlight coming through windows or overhead room light.
Ambient Temperature
The temperature of the encompassing atmosphere, including the environment and air surrounding the equipment in use.
In a wireless network, a device connected to an antenna to increase the signal strength and amplify weak incoming signals.
Analog Input
Continuous variable input.
Analog Output
An electrical output from a sensor that changes proportionately with any change in input pressure, usually represents temperature, pressure, level, or flow. Has the property of being continuously variable, as opposed to having discrete states. Usually, the electrical current signal is of magnitude 4-20 mA where 4 mA is the minimum point of span and 20 mA is the maximum point of span.
Analog Transmission
The transmission of data as a continuous signal, as opposed to an on/off digital signal.
AND Logic
Decision logic for programming functions, where an output is produced only when all inputs are present.
Angular Deflection
Sound waves, like light waves, are reflected from flat surfaces. It is therefore possible that the reflected sonic beam from an angled surface might be too small for the accurate recognition of a target. The influence of tilting increases when the distance between the sensor and the target increases. This effect can also be used to advantage as shown here to remotely detect a target. The reflector must be large enough and have smooth surfaces and edges.
Switch contact connected to the positive terminal of the power supply.
A device connected to a wireless transceiver that concentrates transmitted and received radio waves to increase signal strength, and increase the effective range of a wireless network.
Anti-Reset Windup
This feature of the PID controller prevents the integral (reset) circuit from operating when the temperature is outside the proportional band, thus stabilizing the system.
One of several kinds of visible electrical discharge between separated contacts of a switch. It is primarily a stream of electrons and is accompanied by incandescent metal vapor.
Approach Direction
The object has to approach the light beam laterally or head-on.
The combination of sensors and actuators using one or two common bus cables considerably reduces the wiring costs. AS-Interface does not require the user to generate additional software to operate the bus system. The simple interface is what sets AS-Interface apart from many other bus systems.
Since July 1, 2003 electrical equipment for hazardous areas may only be sold and installed provided it has been designed according to the ATEX guidelines as laid out in the specification paper 95/9/EG.
Atmospheric Pressure Compensation
Value of atmospheric pressure of process when using Relative Humidity algorithm.
Loss or reduction of beam intensity as a result of environmental factors, dust, humidity, steam etc.
Auto Bias
For bumpless transfer, when transferring from local setpoint to remote setpoint. Auto Bias calculates and adds a bias to remote Setpoint input each time a transfer is made.
Auto (Automatic) Mode:
Mode where the controller calculates the output based its calculation using the error signal (difference between setpoint and PV). Controller automatically adjusts output to maintain setpoint at desired value.
Auto Zeroing Technique
Method used to automatically set the null point on a pressure sensor. This is usually done by using a microprocessor to open a solenoid valve at a predetermined time interval. This references atmospheric pressure to both sides of the pressure sensor chip. The microprocessor reads the output voltage and makes that the new null point. This method is used to eliminate errors due to null offset and null temperature shift.
Automatic Control
System that reacts to change or unbalance in one of its variables by adjusting other variables to restore system to desired balance.
Auxiliary Actuator
Mechanism, sold separately, to provide basic switches with easier means of operation and adjustment and adapt switches to different operating motions by supplying supplemental overtravel.
Auxiliary Output
Generally a millivolt or voltage output configured to represent a controller parameter (PV, input, setpoint, deviation, or control output).
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