ACCURACY -
The limit of
deviation from the set point of a pressure or vacuum switch.
It is usually defined in either pounds per square inch, or percentage
of full scale.
ACTUATION POINT - See SET POINT.
ACTUATION VALUE - The difference between the
set point and the reset point.
ADJUSTABLE RANGE - The range within which the
switch can be set from the lowest to the highest point, usually
expressed in PSI, inches of mercury or PSIA.
BUOYANT FORCE - A body submerged in fluid is
pushed or buoyed up by a force equal in magnitude to the weight
of the displaced fluid. Buoyancy is dependent on both weight
and shape of the float.
CRUSH PRESSURE - The maximum pressure to which
the floats may be exposed without deformation. Tanks containing
liquids are frequently pressurized. Crush pressure varies with
the materials of construction, wall thickness, shape and desired
density.
DEADBAND - The difference between the increasing
and decreasing readings when the switch is operated between set
point and reset point.
DIFFERENTIAL - The mechanical motion lost within
the electrical switch element while it reverses itself. This
is usually greater in high amperage switches than in low amperage
switches.
ELECTRICAL RATINGS - The reed switches are specified
as VA (Volt Amps) or Watts. See Table A.
ELECTRICAL SWITCHING ELEMENT - Opens or closes
an electrical circuit in response to movement from the pressure
or vacuum sensing element. Single pole, double throw (SPDT) snap
action switches are standard, may be used as single pole, single
throw (SPST). NO/NC circuitry is selectable, but it must be specified
at order time.
FLOAT - The liquid level sensor, the portion
of the level switch that rises and falls with the changes in
the level of a liquid. The float contains the magnet used to
operate the reed switch. It is made of various materials and
densities to achieve a material compatibility and to be able
to float in liquids with various specific gravities.
FORM A SWITCH - A single pole single throw electrical
switch - the preferred electrical switch for liquid level devices.
FORM C SWITCH - A single pole double throw electrical
switch.
HYSTERESIS - The difference in pressure or vacuum
switch response to increasing or decreasing pressure or vacuum.
INTERFACE - The surface between two liquids
that have different Specific Gravities, e.g. oil floating on
water.
INTERFACED - A float whose buoyancy has been
adjusted to float at the interface of the two liquids that have
different Specific Gravities.
LIQUID LEVEL SWITCH - An electromechanical device
that opens or closes an electrical circuit in response to a change
in the level of a liquid.
LIQUID LEVEL SWITCH OPERATION - A float containing
a permanent magnet riding on the surface of a liquid. The motion
of the float is guided by a stem. The stem contain a reed switch
that is actuated by the magnet in the float.
MOISTURE PROTECTION - Our liquid level switches
are sealed with potting compound. The only path for liquid to
the electrical switch would be through the wires. If the wires
are terminated in an appropriate manner (e.g. - NEMA VI connectors),
the level switch will meet or exceed NEMA VI.
NEMA VI - A device suitable for submersion.
NORMALLY CLOSED SWITCHING ELEMENT - Current
flows through the switch until it is broken by a pressure or
vacuum change.
NORMALLY OPEN SWITCHING ELEMENT - No current
flows through the switch until contact is made by a pressure
or vacuum change.
PRESSURE, ABSOLUTE - A pressure scale based
on PSIA "0" or a perfect vacuum.
PRESSURE, AMBIENT - The pressure immediately
surrounding a pressure switch. It is usually, but not necessarily,
atmospheric gauge pressure.
PRESSURE, ATMOSPHERIC - The pressure caused
by the actual weight of the earth's atmosphere. At sea level,
atmospheric pressure equals 14.7 psi, 30 inches of mercury, or
408 inches of water, above absolute "0" ("0" PSIA).
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PRESSURE, BAROMETRIC -
Actual atmospheric pressure in a specified location and altitude.
The standard is 29.22 inches of mercury at sea level at 70єF.
PRESSURE, DIFFERENTIAL - The difference between
a reference pressure and a variable pressure.
PRESSURE, GAUGE - Uses atmospheric pressure
as a zero reference point so there is no compensation for changes
in barometric pressure.
PRESSURE, MAXIMUM SYSTEM - System pressure,
including surges or spikes.
PRESSURE, PROOF - The maximum pressure which
can be applied to a pressure switch without causing irreparable
damage. It is usually 150% of the pressure sensing element's
rated maximum system pressure.
PRESSURE, SYSTEM - Normal system pressure level
not including surges or spikes.
PRESSURE SENSING ELEMENT - The portion of the
pressure switch that moves with a change in system fluid pressure.
Whitman Controls pressure switches employ capsule, diaphragm,
and piston sensing elements.
PRESSURE SWITCH - An instrument that converts
a pressure change to an electrical function.
REED SWITCH - A hermetically sealed magnetically
operated electrical switch.
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 can return to
its original position.
RESET DIFFERENTIAL - The difference between
the set point and the reset point. It is caused by the hysteresis
of the pressure or vacuum sensing element and the differential
of the electrical switch. This is a fixed function of the switch
and is not adjustable.
RESPONSE TIME (REACTION TIME) - The amount of
time taken between a change in the pressure of the system, and
the change in the electrical signal.
SET POINT - The exact
point at which the electrical switching element functions. This
is generally expressed in PSI, inches of mercury, or PSIA.
SET POINT RANGE - The range within which the
switch can be set from the lowest to the highest point, usually
expressed in PSI, inches of mercury, or PSIA.
SPECIFIC GRAVITY - The ratio of the mass of
the liquid to the mass of an equal volume of water at a standard
temperature, typically 60єF. Liquids with a Specific Gravity
less than one will float on water. Those with a Specific Gravity
greater than one will sink in water.
WORKING PROOF - Maximum pressure which can be
applied to a presure switch without causing set point shift.
| Table
One - Typical Specific Gravities |
| Acetone |
.791 |
| Alcohol, ethyl |
.789 |
| Alcohol, methyl |
.796 |
| Antifreeze |
1.05 - 1.13 |
| Benzene |
.899 |
| Hydraulic Oil |
.900 |
| Gasoline |
.66 - .69 |
| Glycerine |
1.26 |
| Kerosene |
.82 |
| Mineral Oils |
.88 - .94 |
| Muriatic Acid |
1.20 |
| Nitric Acid |
1.50 |
| Sea Water |
1.02 - 1.03 |
| Sulphuric Acid |
1.80 |
| Vegetable Oils |
.91 - .94 |
| Water |
1.00 |
Note:
Specific Gravities can change significantly with temperature. |
STEM - The portion of a liquid level device
about which the float slides. It contains the reed switch,
and provides the exit from the tank for the electrical wires.
They are made of various materials to achieve material compatibility.
SWITCHING CURRENT, MAXIMUM - The maximum load
(amperage) that the electrical switch will carry.
TEMPERATURE, AMBIENT - The temperature immediately
surrounding a pressure switch.
TEMPERATURE SHIFT - A change in switch set
point due to changes in ambient temperature.
VACUUM - Gauge pressure less than ambient
pressure using ambient pressure as a reference.
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