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Lake Shore Model 325 Temperature Controller User’s Manual
Glossary of Terminology A-5
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.
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.
precision . Careful measurement under controlled conditions that 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 that 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 cryogen is boiled off, and the magnet power supply is shut down due to the
sudden increase in current demand.
relief valve . A type of pressure relief device which is designed to relieve excessive pressure, and to re-close and reseal to prevent
further flow of gas from the cylinder after reseating pressure has been achieved.
remanence . The remaining magnetic induction in a magnetic material when the material is first saturated and then the applied field is
reduced to zero. The remanence would be the upper limit to values for the remanent induction. Note that no strict convention exists
for the use of remanent induction and remanence and in some contexts the two terms may be used interchangeably.
remanent induction . The remaining magnetic induction in a magnetic material after an applied field is reduced to zero. Also see
remanence.
repeatability . The closeness of agreement among repeated measurements of the same variable under the same conditions.
2
resistance temperature detector (RTD) . Resistive sensors whose electrical resistance is a known function of the temperature, made
of, e.g., carbon-glass, germanium, platinum, or rhodium-iron.
resolution . The degree to which nearly equal values of a quantity can be discriminated.
2
display resolution . The resolution of the physical display of an instrument. This is not always the same as the measurement
resolution of the instrument. Decimal display resolution specified as " n digits" has 10
n
possible display values. A resolution of n
and one-half digits has 2 × 10
n
possible values.
measurement resolution . The ability of an instrument to resolve a measured quantity. For digital instrumentation this is often
defined by the analog to digital converter being used. A n-bit converter can resolve one part in 2
n
. The smallest signal change that
can be measured is the full-scale input divided by 2
n
for any given range. Resolution should not be confused with accuracy.
RhFe . Rhodium-iron. Rhodium alloyed with less than one atomic percent iron is used to make the Lake Shore RF family of sensors.
Rhodium-iron is a spin fluctuation alloy that has a significant temperature coefficient of resistance below 20 K where most metals
rapidly lose sensitivity.
root mean square (RMS) . The square root of the time average of the square of a quantity; for a periodic quantity the average is taken
over one complete cycle. Also known as effective value.
1
room-temperature compensation . Thermocouples are a differential measurement device. Their signal represents the difference in
temperature between their ends. An ice bath is often used to reference the measurement end to 0 °Celsius so most curves are
normalized to that temperature. Room-temperature compensation replaces an ice bath by monitoring the temperature of the
thermocouple terminals and normalizing the reading mathematically.
RS-232C . Bi-directional computer serial interface standard defined by the Electronic Industries Association (EIA). The interface is
single-ended and non-addressable.