Applications/Processing Guide
ABSOLUTE MINIMUM RESISTANCE: The resistance measured
between the wiper terminal and each end terminal with the
wiper positioned to give a minimum value.
END RESISTANCE: The resistance measured between the wiper ter-
minal and an end terminal when the wiper is positioned at the
corresponding end of mechanical travel. Absolute minimum
resistance and end resistance are synonymous for continuous
rotation trimmers.
TEMPERATURE COEFFICIENT OF RESISTANCE: The unit change in
resistance per degree Celsius change from a reference temper-
ature, expressed in parts per million per degree Celsius as
follows:
TABLE II
Test Current (±20%)
30 ma
5 ma
1 ma
200 ua
50 ua
Total Resistance Range
2 = Rt = 200
200 ‹ Rt = 3K
3K ‹ Rt = 200K
200K ‹ Rt = 1 megohm
1 megohm ‹ Rt = 5 megohm
R
2
– R
1
TC = ——————— X 10
6
R
1
(T
2
– T
1
)
Where:
R1 = Resistance at reference temperature in ohms.
R2 = Resistance at test temperature in ohms.
T1 = Reference temperature in degrees Celsius.
T2 = Test temperature in degrees Celsius.
RESISTANCE-TEMPERATURE CHARACTERISTIC: The difference
between the total resistance values measured at a reference
temperature of 25ºC and the specified test temperature
expressed as a percent of the Total Resistance.
EQUIVALENT NOISE RESISTANCE: Wirewound only. Any spurious
variation in the electrical output not present in the input, defined
quantitatively in terms of an equivalent parasitic, transient resis-
tance in ohms, appearing between the contact and the resistant
element when the shaft is rotated. The equivalent Noise
Resistance is defined independently of the resolution, function-
al characteristics and the total travel. The magnitude of the
Equivalent Noise Resistance is the maximum departure from a
specific reference line. The wiper of the potentiometer is
required to be excited by a specific current and moved at a
specific speed.
TEST TRIMMER
1
3
2
R –R
RTC = ——————— X 100
R
1
2
1
1 ma
SCOPE
OR EQUIVALENT
DETECTOR
CALIBRATION
RESISTOR
INPUT Z
10 X Rt
Where:
R1 = Resistance at reference temperature (25ºC) in ohms.
R2 = Resistance at the test temperature in ohms.
CONTACT RESISTANCE VARIATION: The apparent resistance seen
between the wiper and the resistance element when the wiper
is energized with a specified current and moved over the
adjustment travel in either direction at a constant speed. The
output variations are measured over a specified frequency
bandwidth, exclusive of the effects due to roll-on or roll-off of
the terminations and is expressed in ohms or % of total resis-
tance.
CONSTANT
CURRENT
SOURCE
NOT TO EXCEED
RATING OF R
t
BEING TESTED
ENR (ohms) =
Max. deviation (volts)
.001 amps
CONTINUITY: Continuity is the maintenance of continuous electrical
contact between the wiper and both end terminals of the resis-
tive element.
SETTING STABILITY: The amount of change in the output voltage,
without readjustment, expressed as a percentage of the total
applied voltage.
DIELECTRIC STRENGTH: The ability to withstand the application of
a specified potential of a given characteristic, between the ter-
minals and all other external conducting members such as
shaft, housing and mounting hardware without exceeding a
specified leakage current value.
1
2
Rt
v
3
AC
AMPLIFIER
OR FILTER
OSCILLOSCOPE
CALIBRATION
DECADES
SEE NOTE
INSULATION RESISTANCE: The resistance to a specified DC voltage
impressed between the terminals and all other external
conducting members such as shaft, housing and mounting
hardware.
POWER RATING: The maximum power that a trimming potentiometer
can dissipate across the total resistive element under specified
conditions while meeting specified performance requirements.
ROTATIONAL LIFE: The number of cycles obtainable under specified
operating conditions while remaining within specified allowable
degradation. A cycle is defined as one complete traversal of the
wiper over the resistive element in both directions.
LOAD LIFE: The number of hours at which a device may dissipate
rated power under specified operating conditions while remain-
ing within specified allowable degradations.
ADJUSTABILITY (OUTPUT RESISTANCE): The precision with which
the output resistance of a device can be set to the desired
value.
OUTPUT DETECTOR
Figure 1. Contact-resistance-variation measuring circuit
Rt = Test specimen
Output detector bandwidth: 100 cycles to 50 kilocycles
Minimum input impedance to output detector:
At least 10 times the nominal resistance being tested
NOTE: At the calibration of the decade, terminals 1 and 2 must be
coincident. Calibration decade is to be set for the contact-resistance
variation (CRV) level of the specified nominal resistance being tested.
87
Specifications are subject to change without notice.
BOURNS [ BOURNS ELECTRONIC SOLUTIONS ]
