Pilgrim MULTIFUNCTION PRESSURE AND TEMPERATURE SWITCHES - Manual (Page 9)

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Accuracy – (See repeatability). Accuracy nor-
mally refers to conformity of an indicated value
to an accepted standard value. There is no in-
dication in switch products; thus, instead, the
term repeatability is used as the key perfor-
mance measure.
Automatic Reset Switch – Switch which re-
turns to normal state when the actuating vari-
able (pressure or temperature) is reduced.
Adjustable or Operating Range – That part of
the nominal range over which the switch
setpoint can be adjusted. Normally about 15%
to 100% Of the nominal range for pressure and
differential pressure switches, and the full
span for temperature switches.
Burst Pressure – The maximum pressure that
may be applied to a pressure switch without
causing leakage or rupture. This is normally at
least 400% of nominal range for Ashcroft
switches. Switches subjected to pressures
above the nominal range can be permanently
damaged.
Deadband – The difference between the
setpoint and the reset point, normally ex-
pressed in units of the actuating variable.
Sometimes referred to as differential.
Division 1 – A National Electrical Code Classi-
fication of hazardous locations. In Division 1
locations, hazardous concentrations of flam-
mable gases or vapors exist continuously, in-
termittently or periodically under normal con-
ditions; frequently because of repair or mainte-
nance operation/leakage or due to breakdown
or faulty operation of equipment or processes
which might also cause simultaneous failure of
electrical equipment. Explosion-proof NEMA
7/9 enclosures are required in Division 1
locations.
Division 2 – A National Electrical Code Classi-
fication of hazardous locations. In Division 2
hazardous locations, flammable or volatile liq-
uid or flammable gases are handled, processed
or used, but will normally be confined within
closed containers or closed systems from
which they can escape only in case of acciden-
tal rupture or breakdown or in case of abnor-
mal operation of equipment. Either NEMA 7/9
explosion-proof enclosures or any enclosure
with hermetically sealed switch contacts may
be used in Division 2 locations.
Explosion Proof – A term commonly used in
industry referring to enclosures capable of
withstanding an internal explosion of a speci-
fied gas without igniting surrounding gases.
Strict installation practices in accordance with
the national electrical code is also required for
safety.
Fixed Deadband – The difference between the
setpoint and the reset point of a pressure or
temperature switch. It further signifies that this
deadband is a fixed function of the pressure
switch and not adjustable.
Hermetically Sealed Switch – A switch ele-
ment whose contacts are completely sealed
from the environment to provide additional
safety and reliability. Contact arc cannot cause
an explosion and atmospheric corrosive ele-
ments cannot affect the contacts.
Manual Reset Switch – Pressure or Tempera-
ture switch in which contacts remain actuated
even after the actuating variable returns to nor-
mal. On Ashcroft manual reset switches, a
button must be pushed to reset the contacts.
National Electrical Manufacturers Associa-
tion (NEMA) – This group has defined several
categories of enclosures, usually referred to as
"types." Further, they designate certain features
and capabilities each type must include. For
example, among other features, a NEMA 4 en-
closure must include a threaded conduit con-
nector, external mounting provision and cover
gaskets. When selecting a NEMA 4 enclosure
from any manufacturer, a buyer is assured of
receiving these features.
NEMA 4 – Watertight and dusttight enclosures
intended for use indoors or outdoors to protect
the equipment against splashing, falling or
hose-directed water, external condensation
and water seepage. They are also sleet-resistant.
NEMA 4X – Watertight, dusttight and corrosion
resistant enclosures with same qualifications
as NEMA 4, but with added corrosion resis-
tance.
NEMA 7 – Enclosures for indoor Class I, Divi-
sion 1 Hazardous locations with gas or vapor
atmospheres.
NEMA 9 – Enclosures for indoor Class II, Divi-
sion 1 hazardous locations with combustible
dust atmospheres.
Normal Switch Position – Contact position be-
fore actuating pressure (or variable) is applied,
Normally closed contacts open when the
switch is actuated. Normally open contacts
close when the switch is actuated
Normally Closed – Refers to switch contacts
that are closed in the normal switch state or
position (unactuated). A pressure change
opens the contacts.
Normally Open Switch – Refers to the con-
tacts that are open in the normal switch state
or position (unactuated). A pressure change
closes the contacts.
Overpressure Rating(s) – A nonspecific term
that could refer to either burst or proof pres-
sure, or both.
Proof Pressure – The maximum pressure
which may be applied without causing dam-
age. This is determined under strict laboratory
conditions including controlled rate of change
and temperature. This value is for reference
only. Consult factory for applications where
switch must operate at pressures above nomi-
nal range.
Repeatability (Accuracy) – The closeness of
agreement among a number of consecutive
measurements of the output for the same
value of the input under the same operating
conditions, approaching from the same direc-
tion, for full range traverses.
Note: It is usually measured as nonrepeatability
and expressed as repeatability in percent of
span or nominal range. It does not include
hysteresis or deadband.
Reset Point – The reset point is the pressure,
temperature or differential pressure value
where the electrical switch contacts will return
to their original or normal position after the
switch has activated.
Setpoint – The setpoint is the pressure, tem-
perature or differential pressure value at which
the electrical circuit of a switch will change
state or actuate. It should be specified either
on increase or decrease of that variable. (See
also reset point.)
Single Pole Double Throw (SPDT) Switching
Element – A SPDT switching element has one
normally open, one normally closed, and one
common terminal. The switch can be wired
with the circuit normally open (N/O), or nor-
mally closed (N/C), or both. SPDT is standard
with most Ashcroft pressure and temperature
switches.
Snap Action – In switch terminology, snap
action generally refers to the action of contacts
in the switch element. These contacts open
and close quickly and snap closed with suffi-
cient force to firmly establish an electrical cir-
cuit. The term distinguishes products from
mercury bottle types that were subject to
vibration problems.
Static Pressure – For differential pressure
switches static pressure refers to the lower of
the two pressures applied to the actuator.
SWITCH SELECTION INFORMATION