Lake Shore Model 321 Autotuning Temperature Controller User’s Manual
A-6
Glossary of Terminology
normalized sensitivity
. For resistors, signal sensitivity (dR/dT) is geometry dependent; i.e., dR/dT scales directly with R;
consequently, very often this sensitivity is normalized by dividing by the measured resistance to give a sensitivity, sT,
in percent change per kelvin. sT = (100/R) (dR/dT) %K, where T is the temp. in kelvin and R is the resistance in
ohms.
normally closed (N.C.)
. A term used for switches and relay contacts. Provides a closed circuit when actuator is in the
free (unenergized) position.
normally open (N.O.)
. A term used for switches and relay contacts. Provides an open circuit when actuator is in the free
(unenergized) position.
O.D.
Outer diameter.
oersted (Oe)
. The cgs unit for the magnetic field strength (H). 1 oersted = 10¾
π
ampere/meter
≈
79.58 ampere/meter.
ohm (
Ω
)
. The SI unit of resistance (and of impedance). The ohm is the resistance of a conductor such that a constant
current of one ampere in it produces a voltage of one volt between its ends.
2
pascal (Pa)
. The SI unit of pressure equal to 1 N/m
2
. Equal to 1.45 × 10
–4
psi, 1.0197 × 10
–5
kg
f
/cm
2
, 7.5 × 10
–3
torr,
4.191 × 10
–3
inches of water, or 1 × 10
–5
bar.
permeability
. Material parameter which is the ratio of the magnetic induction (B) to the magnetic field strength (H):
µ = B/H. Also
see
Initial Permeability and Differential Permeability.
platinum (Pt)
. A common temperature sensing material fabricated from pure platinum to make the Lake Shore PT family
of resistance temperature sensor elements.
polynomial fit
. A mathematical equation used to fit calibration data. Polynomials are constructed of finite sums of terms
of the form
a
i
x
i
, where
a
i
is the
i
th
fit coefficient and
x
i
is some function of the dependent variable.
pop-off
. Another term for relief valve.
positive temperature coefficient (PTC)
. Refers to the sign of the temperature sensitivity. For example, the resistance of
a PTC sensor increases with increasing temperature.
pounds per square inch (psi)
. A unit of pressure. 1 psi = 6.89473 kPa. Variations include psi absolute (psia) measured
relative to vacuum (zero pressure) where one atmosphere pressure equals 14.696 psia and psi gauge (psig) where
gauge measured relative to atmospheric or some other reference pressure.
ppm
. Parts per million, e.g., 4
×
10
–6
is four parts per million.
precision
. Careful measurement under controlled conditions which can be repeated with similar results.
See
repeatability.
Also means that small differences can be detected and measured with confidence.
See
resolution.
prefixes
. SI prefixes used throughout this manual are as follows:
Factor Prefix Symbol
10
24
yotta Y
10
21
zetta Z
10
18
exa E
10
15
peta P
10
12
tera T
10
9
giga G
10
6
mega M
10
3
kilo k
10
2
hecto h
10
1
deka da
Factor Prefix Symbol
10
–1
deci d
10
–2
centi c
10
–3
milli m
10
–6
micro µ
10
–9
nano n
10
–12
pico
p
10
–15
femto f
10
–18
atto
a
10
–21
zepto z
10
–24
yocto y
probe
. A long, thin body containing a sensing element which can be inserted into a system in order to make
measurements. Typically, the measurement is localized to the region near the tip of the probe.
proportional, integral, derivative (PID)
. A control function where output is related to the error signal in three ways.
Proportional (gain) acts on the instantaneous error as a multiplier. Integral (reset) acts on the area of error with
respect to time and can eliminate control offset or droop. Derivative (rate) acts on the rate of change in error to
dampen the system, reducing overshoot.
quench
. A condition where the superconducting magnet goes “normal,” i.e., becomes non-superconductive. When this
happens, the magnet becomes resistive, heat is generated, liquid Helium is boiled off, and the Magnet Power Supply
will shut down due to the sudden increase in current demand.
rack mount
. An instrument is rack mountable when it has permanent or detachable brackets that will allow it to be
securely mounted in a 19-inch instrument rack. A full rack instrument requires the entire width of the rack. Two half
rack instruments will fit horizontally in a rack width.
relief valve
. A type of pressure relief device which is designed to relieve excessive pressure, and to reclose and reseal to
prevent further flow of gas from the cylinder after reseating pressure has been achieved.
