GLOSSARY OF TERMS AND DEFINITIONS

ACCURACY (REPEATABILITY) - Accuracy is the maximum operational set point deviation of a single sensor (a pressure, temperature, or flow switch) under one given set of environmental and operational conditions.

ACTUATION AND DEACTUATION POINT - The actuation point (often referred to as the set point) is the exact point at which the electrical circuit controlled by the switching element is opened (or closed) on increasing pressure, flow or temperature. The deactuation point is the opposite, or the point at which the electrical circuit is closed (or opened) on decreasing pressure or temperature.

ADJUSTABLE RANGE FLOW - The total range within which the actuation set point of a sensor may be adjusted.

AMBIENT TEMPERATURE RANGE - The maximum and minimum temperature that will surround the sensor during use and/or test.

BIFURCATED CONTACTS - Electrical contacts which are divided to provide two pairs of mating contacts connected in parallel to provide increased switching reliability.

CONTACT BOUNCE - The momentary opening and closing of switch electrical contacts that occurs at the time of impact of the moving switch pole to the stationary throw contact.

CRITICAL SET POINT - The critical set point is the set point of the unit which is held to the closest tolerance.

DEAD BAND (DIFFERENTIAL, ACTUATION VALUE) - The pressure difference between the actuation point and the deactuation point of a sensor.

DEAD BREAK - Imperfect snap action in which the normally closed circuit opens before the actuating plunger reaches the operating snap over point, or the normally open circuit opens before the actuating plunger reaches the snap travel release point.

DOUBLE POLE DOUBLE THROW (DPDT) SWITCHING ELEMENT - A DPDT switching element has six electrical terminals. In simple terms, it is two single pole double throw switches operating at the same settings. This type of switch can switch two independent circuits.

DUAL SETTING - A dual setting pressure sensor has two independent electrical switches that are actuated by a shared pressure source. Equivalent to two pressure switches in one package.

EXPLOSION PROOF - A term used when it has been determined that there is negligible risk that the switch will cause an explosion of a flammable gas or vapor within the declared environment. Usually the switch cavity must be sealed or have a long flame path.

FACTORY SET - Tamperproof sensor which can be set only at the factory to customer’s requirements.

FIRE RESISTANT - A pressure sensor that is designed with a high melting point barrier (steel) that will prevent flow of sensed flammable fluid from feeding an externally caused fire.

FLOW SWITCH - A flow switch is a sensor that upon the increase or decrease of a flow, opens or closes one or more electrical switching circuits at a predetermined flow rate.

FLUID - A gas or liquid that alters its shape in response to any applied force and that tends to conform to the outline of its container.

GOLD CONTACTS - Gold contact switching elements are characterized by high corrosion resistance and high reliability in switching low voltage and amperage circuits. They are recommended for intrinsically safe and computer interface circuits.

HERMETIC SEAL - A method of sealing the electrical switching element in a sensor so that it is unaffected by all ambient external corrosive agents and explosive gases and ambient pressures. Sealing must be accomplished by soldering, brazing, welding, and glass to metal fusion/compression.

HYSTERESIS - See Dead Band.

LIMP DIAPHRAGM - A diaphragm that has no rigid structure. This type diaphragm conforms to the shape of the sensing pressure plate.

LOW LEVEL CURRENT - A general term used to indicate that the switching current is in the low milliamp range.

MECHANICAL SHOCK - Mechanical pulse, experienced during normal operation.

NORMALLY CLOSED SWITCHING ELEMENT - Is one in which the terminals are wired so that current can flow through the switching element until the plunger pin is actuated to open the circuit.

NORMALLY OPEN SWITCHING ELEMENT - is one in which the terminals are wired so that current will not flow through the switching element until the plunger pin is actuated to close the circuit.

POLYIMIDE - A polymeric film possessing a unique combination of physical and mechanical properties which include long life, excellent deformation/set resistance, high resistance to temperature extremes, good tensile strength, and outstanding resistance to organic compounds. Polyimide is not recommended for water service above 140°F (60°C).

PRESET - Set to a predetermined set point at the factory.

PRESSURE, ABSOLUTE - The difference between zero pressure (a perfect vacuum) and some known pressure. It may be arrived at by adding barometric pressure to gage pressure.

PRESSURE, AMBIENT - The pressure (usually, but not necessarily atmospheric) surrounding a pressure sensor.

PRESSURE, ATMOSPHERIC - The actual weight per unit area of the earth’s atmosphere at a given locale and altitude. Atmospheric pressure at sea level is approximately 14.7 PSI or 30 inches of mercury or 408 inches of water.

PRESSURE, DIFFERENTIAL - The difference between the higher variable pressure and the lower reference pressure.

PRESSURE EXTREMES - The pressure extremes which may be applied to the sensor for short periods under abnormal conditions.

PRESSURE, GAGE - Gage pressure uses atmospheric pressure as a reference, and therefore will vary according to the barometric pressure reading.

PRESSURE, PROOF - Proof pressure (normally 1½ times system pressure ) is the maximum pressure which may be applied to the pressure sensor without causing permanent damage.

PRESSURE (PUMP) RIPPLE - Pump pressure pulsations (usually expressed as peak to peak pressure excursions and frequencies) which adversely affect other components.

PRESSURE SENSING ELEMENT - That portion of the pressure switch that is in contact with and moves as a result of a change in pressure of the fluid. The most common type of pressure sensing elements are diaphragms and pistons.

PRESSURE SNUBBER - Protective device that reduces high pressure rise rates and pump (ripple) pulsations.

PRESSURE SPIKE - Peak pressure resulting from rapid pressure changes caused by high fluid velocity.

PRESSURE SURGE - Peak pressure resulting from any phase of system operation.

PRESSURE SWITCH - A sensor that upon the increase or decrease of a pressure or vacuum, opens or closes one or more electrical switching circuits at a predetermined set point.

PRESSURE, SYSTEM - The nominal pressure level that a system will operate at including work load.

PROOF TEMPERATURE - The maximum temperature of the media which the sensing portion of the switch can be subjected to without causing permanent damage.

REPEATABILITY - The ability of the switch to actuate repeatedly within the specified set points.

RESPONSE TIME OR TIME CONSTANT - The amount of time (in seconds) in which the sensor operates after being subjected to a step temperature increase where the difference between the initial soak temperature and actuation temperature equals 63% of the step temperature. The response time is expressed for a designated media flow (flow rate per second) and system pressure (PSIG).

RISE RATE (PRESSURE) - The rate of media pressure increase in a unit of time, usually referred to as pounds per square inch per second (PSI/sec).

RISE RATE OR RAMP RATE (TEMPERATURE) - The number of degrees (Fahrenheit or Celsius) that the media will increase in a unit of time (minute or second).

SEISMIC SHOCK - Low frequency, high amplitude waves produced as a result of earth movement. Hydra-Electric pressure sensors are generally unaffected by seismic shock and vibration.

SET POINT - See Actuation and Deactuation Point.

SINGLE POLE DOUBLE THROW (SPDT) SWITCHING ELEMENT - A SPDT switching element has one normally open, one normally closed and one common terminal. Three terminals mean that the switch can be wired with the circuit either normally open (N/O or normally closed (N/C).

SWITCH CHATTER - The momentary opening and closing of switch contacts caused by exterior vibration and mechanical shock loads.

SWITCHING CURRENT, MAXIMUM - The maximum load (amperage) that the electrical switch will carry.

TEMPERATURE LAG - The number of degrees above the actuation point that the media will be when the sensor operates. The lag is expressed for a designated rise rate (degrees per second), flow (feet per second), and system pressure (PSIG). The lag is determined by multiplying the rise rate by the response time. Example: If a system with a constant flow, pressure, and rise rate of 10°F per second incorporated a sensor with a response time of 3 seconds, the lag would be 30 degrees.

TEMPERATURE SWITCH - A temperature switch is a sensor that upon the increase or decrease of a temperature, opens or closes one or more electrical switching circuits at a predetermined set point.

VIBRATION RESISTANCE - The vibration test levels (vibratory motion in the three major orthogonal axes) to which the switch assembly shall be exposed.

WETTED PARTS - Materials in a sensor that are directly exposed to the media.