Glossary of Common Industry Terms

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).
Absorption: Diffusion process in which molecules are transferred from the gas phase to a liquid
AC/DC Output: Outputs the AC or DC signal to a data acquisition system or chart recorder.
ACGIH: American Conference of Governmental Industrial Hygienists, which develops and publishes recommended occupational exposure limits for hundreds of chemical substances and physical agents.
AC Line Frequency: The frequency of the alternating current power line measured in Hertz (Hz), usually 50 or 60Hz.
Acid: Any chemical with a low pH that in water solution can burn the skin or eyes. Acids turn litmus paper red and have pH values of 0 to 6.
Acceleration: 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.
Accuracy: 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.
Action: The response of an output when the process variable is changed. See also direct action, reverse action.
Action Level: Term used by OSHA and NIOSH to express the level of toxicant which requires medical surveillance, usually one half of the PEL.
Activated Alumina: A highly porous chemisorbent media - usually impregnated with KMnO4
Activated Charcoal: Charcoal is an amorphous form of carbon formed by burning wood, nutshells, animal bones, and other carbonaceous materials. Charcoal becomes activated by heating it with steam to 800-900° C. During this treatment, a porous, submicroscopic internal structure is formed which gives it an extensive internal surface area. Commonly used as a gas or vapor adsorbent in air-purifying respirators and as a solid sorbent in air-sampling.
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.
Actual: The present value of the controlled variable.
Actuation Signal: Setpoint minus controlled variable at a given instant.
Actuator: 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.
Acute Effect: A change that occurs in the body within a relatively short time (minutes, hours, days) following exposure to a substance. Adverse effect on a human or animal which has severe symptoms developing rapidly and coming quickly to a crisis. Also see "chronic effect."
Acute Exposure: A single exposure to a hazardous agent.
Address: 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.
Administrative Controls: Methods used to control employee exposure to airborne contaminants, e.g., by job rotation or work re-assignment
Adsorbents: Gas scrubbing, porous materials with a very high ratio of interior surface area to external surface area, e.g. (a) activated carbon: the most common adsorbent material due to inherently high surface area and relatively low cost, (b) blended media: mixture of chemically impregnated activated carbon and activated alumina
Adsorption: a physical process in which a gas or vapor adheres to the surface of a solid (usually a highly porous material, e.g., activated carbon. The condensation of gases, liquids, or dissolved substances on the surfaces of solids.
Aerosols: A suspension of solid or liquid particles in air; typical aerosols: (a) Dusts: Solid aerosols generated from the reduction of larger materials; airborne dust range, 0.1 to 30µ, (b) Fumes: Solid aerosols formed by the condensation of solid materials, e.g., welding fumes, range, 0.001 to 1.0µ (c) Smoke: Aerosol mixture formed from incomplete combustion of organic matter, size range, 0.01 to 1.0, (d) Vapors: Gases formed by the evaporation of materials which are normally liquid or solid, size 0.005µ, (e) Gas: materials with the tendency to expand indefinitely and which completely and uniformly fills the container it occupies.
Agent: Any substance, force, organism or influence that affects the body, a part of the body, or any of its functions. The effects may be beneficial or harmful.
AIHA: American Industrial Hygiene Association.
Air: The mixture of gases that surrounds the earth; its major components are as follows: 78.08% nitrogen, 20.95% oxygen, 0.03% carbon dioxide, and 0.93% argon. Water vapor (humidity) varies.
Air Purifier: A device to capture and contain industrial process air contaminants
Air Stream: The narrow sonic beam angle may be affected by strong air streams in excess of 10 m/second.
Air-Line Respirator: A respirator that is connected to a compressed breathing air source by a hose of small inside diameter. The air is delivered continuously or intermittently in a sufficient volume to meet the wearer's breathing requirements.
Air-Purifying Respirator: A respirator that uses chemicals to remove specific gases and vapors form the air or that uses a mechanical filter to remove particulate matter. An air- purifying respirator must only be used when there is sufficient oxygen to sustain life and the air contaminant level is below the concentration limits of the device.
AIT: Auto Ignition Temperature.
Alarm: 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.
Alkali: Any chemical with a high pH that in water solution is irritating or caustic to the skin. Strong alkalies in solution are corrosive to the skin and mucous membranes. Alkalis turn litmus paper blue and have pH values from 8 to 14. Also called base.
Allergy: An abnormal response of a hypersensitive person to chemical and physical stimuli. Allergic manifestations of major importance occur in about 10 percent of the population.
Alternating Current: Electrical current that reverses its direction of flow at regular intervals and has alternately positive and negative values.
Ambient: 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.
Amplifier: In a wireless network, a device connected to an antenna to increase the signal strength and amplify weak incoming signals.
American Conference of Governmental Industrial Hygienists (ACGIH): An organization of industrial hygiene professionals that develops occupational health and safety programs. ACGIH develops and publishes recommended occupational exposure limits for hundreds of chemical substances and physical agents (see Threshold Limit Value).
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.
Anode: Switch contact connected to the positive terminal of the power supply.
ANSI: American National Standards Institute, a voluntary membership organization that develops consensus standards nationally for a wide variety of devices and procedures.
Antenna: 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.
Apparatus Group: The classification of flammable gases into groups that are associated with required apparatus design standards.
Arc: 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.
Area Sampling: Collection and analysis of representative samples of air in general work areas in order to determine the concentrations of any contaminants that are present.
Approach Direction: The object has to approach the light beam laterally or head-on.
AS-Interface: 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.
Asphyxiant: A vapor or gas that can either reduce the oxygen content in the air or interfere with the body’s ability to use oxygen. Exposure to an asphyxiant can result in unconsciousness or death due to being unable to breathe. One of the principal potential hazards of working in confined spaces.
Asphyxiation: Death resulting from lack of Oxygen.
ASTM: American Society for Testing and Materials.
ATEX: European Explosive Atmospheres Directives (ATmospheres EXplosibles). 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.
Atmosphere-Supplying Respirator: A respirator that provides breathing air from a source independent of the surrounding atmosphere. There are two types: air-line and self-contained breathing apparatus.
Atmospheric Pressure: The pressure exerted in all directions by the atmosphere. At sea level, mean atmospheric pressure is 29.92 inches Hg, 14.7 psi, or 407 inches w.g.
Atmospheric Pressure Compensation: Value of atmospheric pressure of process when using Relative Humidity algorithm.
Attenuation: A decrease in signal magnitude from one point to another, or the process causing this decrease. Loss or reduction of beam intensity as a result of environmental factors, dust, humidity, steam etc.
Audiometric Testing: Tests that are conducted to determine the hearing ability of a person. These tests may be used to establish an employee’s baseline hearing, to identify any subsequent hearing loss, and to monitor the effectiveness of noise controls.
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).

Background Suppression: The ability of a special set of photo electric sensors to distinguish targets against various backgrounds and of various colors.
Balancing by Dampers: Design process for local exhaust systems using adjustable dampers to distribute airflow
Balancing by Static Pressure: Design process for local exhaust systems using selected duct diameters to generate static pressures to provide distributed airflow without dampers
Bandwidth: A range of frequencies defined by an upper band-edge frequency, f2, and a lower band-edge frequency, f1. The bandwidth is the difference between the two frequencies (f2 - f1 Hz).
Banking Screw: Banking screws - made of hardened steel - provide limited mechanical protection to the inductive sensors buried therein when hit by an object. Advantage: very robust, quick and easy change of sensors.
Barrier Cream: A cream designed to protect the hands and other parts of the skin from exposure to harmful agents. Also known as protective hand cream.
Base: A compound that reacts with an acid to form a salt. It is another term for alkali.
BASEEFA: British Approvals Service for Electrical Equipment in Flammable Atmospheres. UK Safety Certification
Basic Switch: Self-contained switching unit. It can be used alone, gang-mounted, built into assemblies or enclosed in metal housings.
Baud Rate: The rate of information transfer in serial communications, measured in bits per second.
Benign: Not malignant. A benign tumor is one which does not metastasize or invade tissue. Benign tumors may still be lethal, due to pressure on vital organs.
Best Fit Straight Line (BFSL): Method for defining linearity. A straight line placed on a sensor output curve such that half the data points lie above and half below that line. The method for determining BFSL, is the sum of least squares.
Bias: Compensate input for drift of an input value due to deterioration of a sensor or other cause.
Bidirectional Differential Pressure Sensor: Differential pressure sensor allowing the greater input pressure to be applied to either pressure port.
Bilateral Work Stoppage: Stoppage of work under the direction of the worker certified member and the management certified member when both members have reason to believe that dangerous circumstances exist.
Binary Code: This code type is constructed similarly to the decimal system, but has only the digit values "0" and "1".
Binary Coded Decimal (BCD) Code: To avoid converting a decimal number into a binary number, instead of using natural binary code, often only the individual digits of the decimal number are encoded in binary.
Biohazard: A combination of the words biological hazard. Organisms or products of organisms that present a risk to humans.
Biological agent: Any living organism (for example, virus or bacteria) that affects the body, a part of the body, or any of its functions. The effects may be beneficial or harmful.
Biological monitoring: The use of medical tests (for example, blood, urine, exhaled air) to determine whether a person has been or is being exposed to a substance.
Blackbody: An ideal surface that absorbs all incident radiation, regardless of wavelength, the direction of incidence and polarization. It radiates the maximum energy possible for given spectral and temperature conditions. A blackbody has an emissivity of 1.00. See also Emissivity.
Blanking: The emitter sends a short pulsed signal with a relatively long pause between two pulses. The light energy of the LED can therefore be enormously increased. If emitter and receiver are mounted in the same housing, the receiver is clocked to the emitted pulse. Interference is therefore suppressed 98% of the time.
Blind Range ST: Reliable object recognition is not possible within the blind range (St). Objects within this blind range may cause false switching of the sensor.
BMS: Building Management System.
Boiling Point: The temperature at which a liquid changes to a vapor. Also, the temperature at which the vapor pressure of a liquid equals atmospheric pressure.
Bonding: The use of low-resistance material to connect two or more conductive objects that would likely undergo a build-up of static electricity. Bonding prevents the unwanted release of electrical energy, such as sparks. E.g., transferring of one flammable liquid from one container to another can release electrical energy if it is not bonded.
Brake Horsepower: The power needed to spin the fan (neglecting motor/fan drive inefficiencies), 1 HP = 33,000 ft.-lb per min.
Brake Horsepower Curve: Graphical representation of brake HP at different airflow rates for a fan
Branch (or path) of greatest resistance: Path from a hood to the fan (and exhaust stack if used) that causes the greatest pressure loss in duct system
Break: To open an electrical circuit.
Break Distance: Minimum distance between separated mating contacts in their fully open position.
Breathing Zone: The area surrounding the worker’s head. The make-up of air in this area is thought to be representative of the air that is actually breathed in by the worker. Used for toxic gas monitoring.
Breathing Zone Sample: Air samples collected in a worker’s breathing zone to assess inhalation exposure to airborne contaminants.
Bridge circuit: Wheatstone Bridge circuit used in catalytic detector design.
British Thermal Unit (BTU): In specific terms, a BTU is the amount of energy required to heat one pound of water (beginning at 60 degrees F and 14.696 psia) one degree Fahrenheit. An easier way to visualize this amount of energy is to burn a standard wooden match stick. The full burning of the match stick releases approximately one BTU.
Broadband: Broadband measurements from a sound level meter refer to measurements made over the applicable frequency range of the instrument.
Bump Test: Check of basic functionality by exposure to test gas, resulting in a gas indication or alarm condition.
Bumpless Transfer: Change from manual mode to automatic mode of control, or vice versa, without change in control signal to the process.
Burnout (Sensor Break Protection): If input fails, indicated PV signal increases (upscale) or decreases (downscale) with indication on the interface.
Burst Fire: A power control method that repeatedly turns ON and OFF full AC cycles. Also called zero-cross fire, it switches close to the zero-voltage point of the AC sine wave. Variable-time-base burst fire selectively holds or transits AC cycles to achieve the desired power level.
Burst Pressure: Specified pressure that will rupture the sensing element but not the sensor case.
Byproduct: The product formed or released by a material during use in a process. This is produced in addition to the principle product. A by-product may be toxic, flammable or explosive.

CA

An SPL average that enhances the low frequency components of the sound signal. The measurement is used to evaluate hearing protection and other noise reduction devices.

Calibrate

Adjusting instrument for proper response.

Calibration

The comparison of a measuring device (an unknown) against an equal or better standard. Test during which known values of Measurand are applied to the device under test and corresponding output readings are recorded under specified conditions. The process of adjusting the output of the detector to give an accurate reading of gas concentration over its measuring range.

Calibration Curve

Graphical representation of the calibration record.

Calibration Cycle

the application of known values of Measurand and recording of corresponding Output readings over the full or the specified portion of the Range, in an ascending and descending direction.

Calibration Offset

An adjustment to eliminate the difference between the indicated value and the actual value.

Capacitance

Change in energy or material required to make a unit change in a measured variable.

Capacitance Cs, Cause of Change

- Proximity to conductive objects

If an object of conductive material is located within the sensing distance of the sensor, it will form two series connected capacitances with sensor areas S and M. The series connected capacitances are much larger than the capacitance of the undamped oscillator. Maximum sensing distance can be achieved with conductive objects like metals, water etc.

- Of non-conductive objects

If a non-conductive object is moved into the sensor field, the field will be amplified in relation to the relative permittivity (Er) of the material to be detected and thus increase capacitance Cs. As from a relative permittivity of Er = 81 (water), sensing distances can be achieved that are equivalent to those for conductive materials. The sensing distance is reduced for materials with a lower Er.

Material	Relative Permittivity (Er)	Material	Relative Permittivity (Er)
Air, Vacuum	1	Wood	2-7
Paper	1.2 - 3	Marble	8.4 - 14
Paraffin Oil	2.2	Alcohol	25
PVC	3	Methanol	33.5
Glass	3-5	Water	81

Capacitive Load

Leading load; predominantly capacitive, so voltage does not change direction until corresponding current does.

Capacitive Sensors

Sensing technique which uses the capacitance of a target (can be clear glass or liquids) to switch an output.

Capacitor

Circuit device that can store an electric charge. A typical capacitor has 2 conductors or electrodes separated by a layer of non-conducting material (dielectric). With conductors on opposite sides of the dielectric layer, oppositely charged by a source of voltage, the electrical energy of the charged system is stored in the polarized dielectric.

Capture envelope

A zone in front of a hood within the bounds of which contaminants will move into the hood

Capture velocity

Air velocity at any point in front of a hood necessary to overcome opposing air currents and to capture the contaminated air at that point by causing it to flow into the hood

Carbon monoxide

A colorless, odorless toxic gas produced by any process that involves the incomplete combustion of carbon-containing substances. It is emitted through the exhaust of gasoline powered vehicles.

Carcinogen

A chemical, physical or biological agent capable of causing or producing cancer in mammals, including humans. A chemical is considered to be a carcinogen if a) it has been evaluated by the International Agency for Research on Cancer (IARC) and found to be a carcinogen or potential carcinogen; or b) it is listed as a carcinogen or potential carcinogen in the Annual Report on Carcinogens published by the National Toxicology Program (NTP) (latest edition); or c) it is regulated by OSHA as a carcinogen.

Carcinogenic

Capable of causing Cancer.

CAS number

Chemical Abstracts Service. CAS Registry number used to identify substances without the ambiguity of chemical nomenclature.

Cascade

(a) To combine logic circuitry to get more complex logic or timing control. (Inputs and outputs are wired in series.) (b) Two or more controllers working together. The output of the master controller is the set point for the "slave" controller. A classic example is the control of a reactor (a large vessel with a steel jacket around it). The product temperature (master) controller's output is the setpoint of the jacket temperature (slave) controller.

Cascade Control

Control action where the output of one controller is setpoint of another controller. Can be used in a controller using two loops of control.

Catalyst

A substance that changes the rate of a chemical reaction but is itself not changed. Switch contact material sometimes acts as a catalyst, accelerating the formation of polymers on the contact surface.

Catalytic sensor

For detection of combustible gases. These are made of an electrically heated platinum wire coil, covered first with a ceramic base such as alumina and then with a final outer coating of palladium or rhidium catalyst dispersed in a substrate of thoria.

Cathode

The switch contact connected to the negative terminal of the power supply.

CE-Compliant

Compliant with the essential requirements of European directives pertaining to safety and/or electromagnetic compatibility.

Ceiling limit (C)

An airborne concentration of a toxic substance in the work environment, which should never be exceeded.

Cell

An individual sensor.

Celsius

Formerly known as Centigrade. A temperature scale in which water freezes at 0°C and boils at 100°C at standard atmospheric pressure. The formula for conversion to Fahrenheit scale is: deg°F = (1.8*deg°C) + 32.

CENELEC

Comite Europeen de Normalisation Electrotechnique: a European standards committee, similar to UL or NEMA. It covers standardized dimensions and operating characteristics.

Center frequency

The center frequency of each octave and third octave filter band.

CFM

Unit of air flow measurement, cubic feet per minute

Channel

One line or point of detection or input

Chatter

The rapid On-Off cycling of an electromechanical relay or mercury displacement relay due to insufficient controller bandwidth. It is commonly caused by excessive gain, little hysteresis, and short cycle time.

Chemcassette®

Honeywell registered name of a paper tape cartridge used in toxic gas analyzers.

Chemical agent

A chemical substance that affects the body, a part of the body, or any of its functions. The effects may be beneficial or harmful.

Chemical cartridge respirator

A respirator that uses various chemical substances to purify inhaled air of certain gases and vapors. This type respirator is effective for concentrations no more than ten times the TLV of the contaminant, if the contaminant has warning properties (odor or irritation) below the TLV.

Chemisorption

A non-reversible chemical process, impregnated activated alumina media attracts gaseous contaminants which are converted to non-toxic solids that remain on the pellets and are permanently removed from the environment Differential pressure; the difference in static pressure between two locations, e.g., above and below a filter

Chip

A die (unpackaged semiconductor device) cut from a silicon wafer, incorporating semiconductor circuit elements such as resistors, diodes, transistors, and/or capacitors.

Chronic Effect

An adverse effect or change that occurs in the body over a relatively long time (weeks, months, years) following repeated exposure or a single over-exposure to a substance. Also called an acute effect

Chronic Exposure

Repeated exposure to a hazardous agent.

Class 1/Class 2 Microphones

See "Type 1/Type 2 microphones".

Clean Air

Ideal conditions. Climate-controlled or sterile area.

Clock Frequency (SSI)

For absolute encoders with synchronous serial interface (SSI), the clock frequency is the frequency of the clock signal during data transmission. The clock frequency is specified by the sequence electronics, and must be within the corresponding limits.

Clock + / Clock -

Control lines of the SSI interface for synchronous data transmission. Clock+ and clock- together form a current loop, for potential-free reception of the clock frequency in SSI encoders.

Close Range Shielding

The capacitive sensor responds to all materials whose relative permittivity Er is greater than 1 (air, vacuum). This means that dirt deposits and moisture on the sensor surface are also detected.

Closed Loop

Complete signal path in control system; represented as group of units connected in a manner that signal started at any point follows closed path and comes back to that point. Signal path includes forward path, feedback signal, and summary point.

Closed Loop Control

A control system in which all adjustments necessary to maintain the system occur automatically through a feedback signal from the sensor.

Code of Federal Regulations (CFR)

A collection of the regulations that have been promulgated under United States Law.

Code Reader

A code reader contains up to 6 identical inductive sensors. Advantage: common supply rail, quick installation, reduced distance between individual sensors, very compact

Code Switching Speed

Number of measuring steps per second for absolute multi-turn encoders. For encoders with 13 bit resolution and 400 kHz code switching frequency, the maximum rotational speed is 3,000 rpm.

Co-generation

The term used to express the simultaneous production of two useful forms of energy from one process, i.e. steam used to produce electricity and provide for space heating in the same process.

Cold Junction

Connection point between thermocouple metals and the electronic instrument.

Cold Junction Compensation

Electronic means to compensate for the effective temperature at the cold junction.

Color Sensors

With the color sensor, you can use color as the criteria for sorting, quality monitoring and automation processes.

Combustible

Capable of catching fire and burning, usually a material that has a flash point above 37.8°C. See also flammable.

Combustible liquid

Combustible liquids are those having a flash point at or above 37.8°C (100°F).

Common Mode Rejection (CMR)

The ability of an electronic device to eliminate the effect of AC or DC noise between signal and ground. Normally expressed in dB at DC to 60Hz. See also Normal Mode Rejection.

Communications Address

Number assigned to instrument used in data message exchange.

Community Noise Exposure Level (CNEL)

The CNEL is a 24-hour average sound level, which adds 5dB to noise measured between 7 p.m. and 10 p.m., and adds 10dB to noise measured between 10 p.m. and 7 a.m.

Compensation

Procedure of providing a supplemental device, circuit, or special materials to counteract known sources of error (e.g., ambient temperature change). Compensation is often related to temperature compensation only.

Complementary Output

Both N.O. and N.C. outputs are available for use. A circuit that provides sink or source capability with a single input. Output that can be both light operated and dark operated. (Also known as 4-wire DC controls.)

Composition

A process variable that represents the amount of one material in a solution, or gas.

Concentration

The amount of a given substance in a stated unit of measure. Common methods of stating concentration are percent by weight or by volume, weight per unit volume, normality, etc.

Condensate

When steam cools it first transitions to water vapor and then back into liquid water, the condensed liquid is called condensate.

Conduit

Metal tubing mainly used in the US for installation of wires in hazardous areas.

Configuration

Dedicated operation; keystroke sequences select and establish pertinent control data best suited for an application.

Contaminant

An unwanted material (for example, radioactive, biological or chemical) that is likely to harm the quality of the working environment. The most common workplace contaminants are chemicals that may be present in the form of dusts, fumes, gases or vapors.

Control Cycle

The rate at which the output signal is updated.

Control Action

Nature of change of output affected by input. Output can be signal or value of a manipu-lated variable. Input can be an actuating error signal, output of another controller, or control loop feedback signal when setpoint is constant.

Control Base

Unit remote from sensor in which amplification and conditioning of the input signal takes place. Usually contains a power supply and an output device.

Control Mode

Designates the mode in which controller will operate (such as Manual, Automatic with Local Setpoint, Automatic with Remote Setpoint, Manual Cascade).

Control Point

Value of controlled variable that you operate to maintain.

Controlled Variable

Quantity or condition of controlled medium that is measured and controlled.

Controller

Device that measures changes in controlled variable and indirectly maintains the controlled variable within present limits.

Controller Output – CO

Output signal from the controller.

Controls

Measures designed to eliminate or reduce hazards or hazardous exposures. Examples include engineering controls, administrative controls, personal protective equipment. Hazards can be controlled at the source, along the path to the worker, or at the worker.

Convergent Beam

A variation of the diffuse scanning mode. A photoelectric control whose optical system is key to its operation. It simultaneously focuses and converges a very small, intense beam to a fixed-focal point in front of the control. The control is essentially blind a short distance before and beyond this focal point. Convergent beam scanning is used to detect the presence or absence of small objects while ignoring nearby background surfaces.

Convertible Output

Output that can be wired either as Normally Open or Normally Closed, but not at the same time.

Corner Frequency

For first order time constants, the "corner frequency" is the frequency where the amplitude ratio starts to turn and the phase lag equals 45 degrees.

Corrective Factor

Mathematical factor that, when multiplied by the sensing distance of a given sensor, will adjust sensing distance for the different metals being used as targets.

Corrosive

A substance that causes visible destruction or permanent changes in human skin tissue at the site of contact.

COSHH

Control of Substances Hazardous to Health.

Couplings

The most suitable flexible coupling can be chosen from the data of a servo drive system. Resolution, acceleration and the desired positional precision must be considered. The lag angle can be judged from the torque stiffness. This torque might be considerable, if high dynamic drive systems are used. The inertia moment is specified on the product data pages.

Crest Factor

The ratio of the instantaneous peak value of a wave to its RMS value. This is a performance specification of a meter’s ability to process signals that have peaks that are substantially higher than their RMS averages.

Criterion Level (CL)

Criterion level is the average SPL that will result in a 100% dose over the Criterion time, usually 8 hours. The Criterion Level is typically set by a regulating agency, such as OSHA, and is not usually applicable for community noise monitoring.

Criterion Time (CT)

The time over which the Criterion Level is established, generally 8 hours.

CSA

Canadian Standards Administration

Current

Time value of movement of free electrons. One ampere equals one coulomb per second. Conventional reference is opposite to direction of actual electron movement.

Current Consumption

Amount of current required to power a sensor or control (excluding load). See supply current.

Current Duplex

Control algorithm that provides a second current output (split range) or second current output via auxiliary output for heat cool zones.

Current Sinking

Output type such that when it is On, current flow is from the load into the device's output, then to ground. Output is Normally High. The sensor "sinks" current from the load through the sensor to ground. The load is connected between the positive lead of the supply and the output lead of the sensor.

Current Sourcing

an output type such that when it is On, current flow is from the device into the load. Output is Normally Low. The sensor "sources" current to the load. The load is connected between the output lead and the negative ground lead of the supply.

Current/Time Duplex

Variation of duplex with current active for 50% output and relay active for 50% output.

Cutaneous

Pertaining to or affecting the skin.

Cycle Time

Length of one time-proportional output relay cycle. The time, usually expressed in seconds, for a controller to complete one on/off cycle.