Tuesday, November 21, 2017

Reference Definitions

 

Common Definitions for Pressure and Vaccum Applications

 

Accuracy - The limit of deviation from the set point of a pressure or vacuum switch. It is usually a percentage of full scale.

 

Actuation Point - See Set Point

 

Adjustable Range -The limits between which the set point can be adjusted.

 

Burst Pressure - Pressure which causes failure of the pressure element, resulting in permanent damage.

 

Cycle - One complete sequence of values usually above, and below the set point, which occurs during a time period.

 

Dead-band - The minimum change in pressure required to open or close the contacts of a switch.

 

Differential Pressure- A measured pressure difference between two pressure sources.

 

Electrical Switching Element - Opens or closes an electrical circuit due to a movement from the pressure or vacuum sensing element.

 

Hysteresis - The difference in readings of an instrument when it is approached from two different directions.

 

Maximum System Pressure - The highest pressure that a switch may safely operate at.

 

Maximum Working Pressure - The designed safe limit of a pressure element for regular use a specified pressure.

 

Normally Closed - Current flows through the switch until the contact is broken by a pressure or vacuum change.

 

Normally Open - No current flows through the switch until contact is made by a pressure or vacuum change.

 

NEMA 4 - Water tight and dust tight enclosure.

 

NEMA 4X- Water tight, dust tight, and corrosion resistant enclosure.

 

Pressure, Absolute - A pressure scale based on PSIA “0” or a perfect vacuum.

 

Pressure, Ambient - The pressure immediately surrounding a pressure switch.

 

Pressure, Atmospheric - The pressure caused by the actual weight of the Earth’s atmosphere. At sea level atmospheric pressure equals 14.7 PSI, 30” HG, or 760 Torr.

 

Pressure, Barometric - Actual atmospheric pressure in a specific location.

 

Pressure, Burst – The maximum pressure the unit can withstand without causing a release of the application media.

 

Pressure, Differential - The difference between a reference pressure and a variable pressure.

 

Pressure, Gauge - Uses atmosphere as a zero reference point so there is no compensation for changes in barometric pressure.

 

Pressure, Maximum System - Normal system pressure level not including surges and spikes.

 

Pressure Proof - Pressure in excess of the maximum operating pressure to which the sensor may occasionally be subjected to.

 

Pressure, Sensing Element - The portion of the pressure switch that moves with a change in system fluid pressure. Wasco, Inc. pressure switches use capsule, diaphragm, and piston sensing elements.

 

Pressure, Switch - An instrument that converts a pressure change to an electrical function.

 

Radio Noise - Electromagnetic interference (EMI)

 

Reset Band - The difference in pressure between the set point, and the reset point.

 

Reset Point - Point at which the electrical switching element snaps back to its original position prior to initial actuation.

 

Response Time (Reaction Time)- The amount of time taken between a change in pressure, and a change in the electrical signal.

 

Repeatability - The ability of the switch to actuate repeatedly at the desired set point within the sensors tolerance.

 

Set Point - The exact point at where the electrical switching occurs. This is generally expressed in PSI, or inches, of mercury.

 

Set Point Range- The range from which the switch can be set from the lowest, to the highest point.

 

Switching Current, Maximum - The maximum load (amperage) the electrical switch will carry.

 

Temperature, Ambient - The temperature immediately surrounding a pressure switch.

 

Temperature, Shift - A change in set point due to changes in ambient, or fluid temperatures.

 

Vacuum- The value pressure of below atmospheric pressure.

 

Wetted Parts - Components that come in direct contact with the process media.

 

Working Pressure Range - The pressure range where the sensor can safely operate, and still maintain the set point