Instrumentation & Controls Glossary

• Tags: Instrumentation and Controls Glossary

A        

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• Analog  -  A continuous electronic variable signal caring information.
• Analog Output  -  A signal coming from a PLC into an instrument or controller.
• Automatic Well Test  -  Specified as on instrument bubbles on Piping and Instrumentation Diagram.

B

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• Background Noise  -  Interfering signals that can cause disturbance affecting a signal that may distort the intended signal.
• Backplane  -  A group of electrical connectors in parallel with each other, so that each pin of each connector is linked to the same relative pin of all the other connectors, forming a computer bus.  It is used as a backbone to connect several printed circuit boards together to make up a complete computer system.
• Batch process  -  Any process on which operations are carried out on a limited number of articles, as opposed to continuous process.
• Bus  -  The group of conductors that interconnect individual circuitry in a computer. Typically, a bus is the expansion vehicle to which I/O or other devices are connected. Examples of PC buses are the ISA and PCI buses

C         

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• Cache  -  High-speed processor memory that buffers commonly used instructions or data to increase processing throughput.
• Capacitance  -  The ability to hold an electric charge.
• Car Seal  -  Specified on instrument bubbles on Piping and Instrumentation Diagram.
• Carrier Frequency  -  The transmission of a fixed frequency that has been changed or modified to carry data or information.  The frequency is usually measured in Hertz (cycles per second).
• Channel List  -  A variable length list of channels and their associated gains specifying which analog input channels to convert to digital values.  In continuous A/D acquisition mode, the list wraps around to the first channel after it reaches the end.  The channels need not be in any particular order.
• Current  -  The rate of flow of electricity in a circuit, measured in amperes.  Amp is a unit of current.  One ampere (amp) is the current flowing through one ohm of resistance at one volt potential.
• Current Drive Capability  -  The amount of current a digital or analog output channel is capable of sourcing or sinking while still operating within voltage range specifications.

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• Data Length  -  Indicates the set data format.
• Data Recorder  -  Another name for a data logger, though data recorders are typically higher performance and offer higher sample rates than a typical data logger.
• Differential Pressure Flowmeter  -  There are many different types of instruments for measuring pressure.  The functions of these instruments are to monitor and control pressure in a process stream.
• Differential Set Pressure  -  The pressure difference between the set pressure and constant back pressure.
• Discrete Input  -  Relative to the device that reads either a TRUE or a FALSE, 1 or 0, or ON of OFF as an input signal.

E         

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• Ethernet  -  A family of computer networking technologies for local area networks (LANs) first introduced in 1980.  Systems that use Ethernet for communications divide a stream of data into individual packets called frames.  Each frame contains source and destination addresses and error-checking data so that damaged data can be detected and re-transmitted.
• Electric Current  -  The rate of flow of electricity in a circuit, measured in amperes.
• External Trigger  -  A voltage pulse from an external source that trig- gers an event such as A/D conversion.

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• Filter  -  A device that allows certain parts of a signal to pass through while blocking others.  In data acquisition systems, the most common type of filter used is a low pass, anti-aliasing filter.
• Firewall  -  A device or set of devices designed to permit or deny network transmissions based upon a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass.
  
• Flow Quality Indicating Transmitter  -  , abbreviated as FQIT, is an instrument that is used for measuring the amount of a liquid and a gas in two pase flow.
• Flow Switch  -  Provides a discrete input to the PLC.  The flow switch is typically used as a method of control in tanks, vessels, pumps and other types of process equipment.
• Flowmeter  -  An instrument used to measure the flow rate of gasses and liquids.

G

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• Gain Accuracy  -  A measure of deviation of the gain of an amplifier from the ideal gain.
• Gauge Factor  -  A measure of the ratio of the relative change of resistance to the relative change in length of a piezoresistive strain gage.
• Grounded Junction  -  A form of construction of a thermocouple probe where the hot or measuring junction is in electrical contact with the sheath material so that the sheath and thermocouple will have the same electrical potential.

 

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• Half Bridge  -  Two active elements or strain gages.

I

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• Input Impedance  -  The resistance measured across the excitation terminals of a transducer.
• Insulation Resistance  -  The resistance measured between two insulated points on a transducer when a specific DC voltage is applied at room temperature.
• Integral Control  -  A control action that eliminates the steady-state offset inherent in proportional control.
• Interface  -  The means by which two systems or devices are connected and interact with each other.
• Interrupt  -  A computer signal indicating that the CPU should suspend its current task to service a designated activ- ity.

J

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• Junction  -  The point in a thermocouple where the two dissimilar metals are joined.

K

L

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• Loop Resistance  -  The total resistance of a thermocouple circuit caused by the resistance of the thermocouple wire.  Usually used in reference to analog pyrometers which have typical loop resistance requirements of 10 ohms.

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• Manual Reset  -  The adjustment on a proportioning controller which shifts the proportioning band in relationship to the set point to eliminate droop or offset errors.
• Maximun Operating Temperature  -  The maximum temperature at which an instrument or sensor can be safely operated.
• Maximum Power Rating  -  The maximum power in watts that a device can safely handle.
• Meter  -  A device that provides a measurement for the flow change in a gas or liquid.
• Motherboard  -  The pc board of a computer that contains the bus lines and edge connectors to accommodate other boards in the system.  In a microcomputer, the motherboard contains the microprocessor and connectors for expansion boards.
• Mounting Error  -  The error resultant from installing the transducer, both electrical and mechanical.
• Multiplex  -  A technique which allows different input or output signals to use the same lines at different times, controlled by an external signal.

N

O         

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• Operating System  -  A collection of programs that controls the overall operation of a computer and performs such tasks as assigning places in memory to programs and data, processing interrupts, scheduling jobs and controlling the overall input/output of the system.
• Orifice rea -
• Orifice Center of Head  -
• Orifice Discharge Coefficient  -  The ratio of actual discharge to the theoretical discharge.
• Orifice Flange  -  Meters the volumetric flow rate of liquids and gasses through a pipe.  Two orifice flanges are called an orifice flange union.
• Orifice Flow Rate  -  The amount of fluid that flows in a given time.
• Orifice Gravitational Constant  -
• Orifice Head Loss  -
• Orifice Plate  -  Measures the flow of a liquid or gas by the difference in pressure from the upstream to the downstream.
• Orifice Pressure Loss  -
• Orifices and Nozzles on a Horizontal Plane  -
• Orifices and Nozzles on a Vertical Plane  -
• Output  -  The electrical signal which is produced by an applied input to the transducer.
• Output Impedance  -  The resistance as measured on the output terminals of a pressure transducer.

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• Position Switch  -  Provides a discrete input to the PLC.  The position switch is used to confirm the position of a critical component in the process, often a valve.
• Pressure Differential Transmitter  -  Measures the difference between a high pressure input and a low pressure input.  This can be used to measure process properties such as flow, density, level, viscosity and temperature.
• Pressure Indicating Transmitter  -, abbreviated as PT and PIT, is an instrument for measuring, controlling and indicating positive, negative or differential pressures of different fluids.
• Pressure Indicator  -  It is a field instrument that requires little to no maintenance.
• Pressure Switch  -  A discrete input to the PLC.  The pressure switch is typically used as a method of control in tanks, vessels and over all process control.

Q

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• Repeatability  -  The ability of the switch to actuate repeatedly at the desired set point within sensor tolerance.Reset Point  -  After the pressure has reached set point and operated the electrical switch, it must return to the reset point before the electrical switch returns to its original position.
• Resistance Temperature Detectors  -  A sensor used to measure temperature by correlating the resistance of the element with temperature.

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• Shunt  -  A calibrated low resistance connected in parallel with the input terminals of an ammeter in order to enable measurement of higher currents. It can be internal or external.

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• Temperature Controller  -  An instrument designed to minimize operator input or involvement.  A temperature controller has an input that is connected to a temperature source such as an RTD or other type of temperature element.
• Temperature Differential Switch  -  Contains the same functionality of a temperature switch with the exception that it is looking for the difference of temperature rather than a single input.
• Temperature Recorder  -  A device that records the temperature of a process.  This could be a data logger or a temperature transmitter capable of storing data.
• Temperature Switch  -  Provides alarm, shutdown and control for many types of processes.  Switch that activates when a certain temperature condition is met.
• Termination  -  A load connected to the end of a transmission line.  To avoid signal reflections, it must match the characteristic impedance of the line.
• Thermopile  -  A number of thermocouples connected in series, arranged so that alternate junctions are the referenced temperature and at the measured temperature to increase the output for a given temperature difference between the measuring and reference junctions.
• Thermowell  -  Used in temperature measurement and provide isolation from the temperature sensor and the process fluid.

U

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• Variable Data  -  Numerical information that can be changed during application operation.  It includes timer and counter accumulated values, thumbwheel settings, and arithmetic results.
• Velocity Flowmeter  -
• Volt  -  A unit of electrical pressure.  One volt is the amount of pressure that will cause one ampere of current in one ohm of resistance.
• Voltage  -  The value of electrical potential difference across a conductor expressed in volts.
  

W

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• Watt Density  -  The watts emanating from each square inch of heated surface area of a heater.

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