INSTRUCTION MANUAL
KEPCO
An ISO 9001 Company.
KT
ACCESSORY
CURRENT CONTROL RHEOSTAT
CURRENT SENSING RESISTORS
GENERAL DESCRIPTION (Refer to FIG’s 1 and 2)
Kepco Current Sensing and Control Resistors are precision, wire-wound components with low temperature coefficients. The 4-terminal current sensing resistor (R
nal circuitry needed to convert a d-c voltage stabilizer into a d-c source supplying stabilized output current. The sensing
resistor (R
rheostat (R
), placed in series with the load, provides a voltage drop proportional to the output current. The control
S
) is connected to supply feedback from the sensing resistor to the NULL JUNCTION (INVERTING
CC
INPUT) of the power supply. In this manner, excellent current stabilization can be achieved over a minimum range of
2% to 100% of I
max. where IO max. is the selected maximum power supply output current. (Refer to FIG. 2). The cur-
O
rent sensing resistors can also be used for measuring the output current delivered by the power supply.
) and the 10-turn current control rheostat (RCC) provide all the exter-
S
Kepco Model KT 1304, 0-1000Ω
1W at 65°C, 20 ppm max
See FIG. 4, C for dimensions.
CURRENT FEEDBACK CONTROLTYPICAL 100W RESISTOR (LEADS)TYPICAL 50W RESISTOR (LEADS) TYPICAL 30W RESISTOR (SCREWS)
EQUIPMENT
FIGURE 1. KEPCO CURRENT SENSING RESISTORS AND CONTROL RHEOSTAT
TABLE 1. KEPCO SENSING RESISTORS
MODEL
KT 1915 1.0 LEADS 50W 0.02A 1A SEE FIG. 4, A
KT 1385 0.667 LEADS 50W 0.03A 1.5A SEE FIG. 4, A
KT 1399 0.5 LEADS 50W 0.04A 2A SEE FIG. 4, A
KT 1386 0.333 LEADS 50W 0.06A 3A SEE FIG. 4, A
KT 1598 0.2 LEADS 50W 0.01A 5A SEE FIG. 4, A
KT 2356 0.1 LEADS 50W 0.2A 10A SEE FIG. 4, A
KT 2713 0.01 LEADS 50W
KT 2537 0.0625 LEADS 100W 0.32A 16A SEE FIG. 4, B
KT 2536 0.05 LEADS 100W 0.4A 20A SEE FIG. 4, B
KT 2480 0.033 LEADS 100W 0.6A 30A SEE FIG. 4, B
KT 2330 0.02 LEADS 100W 1A 50A SEE FIG. 4, B
KT 2325 0.01 LEADS 100W 2A 100A SEE FIG. 4, B
KT 2714 0.001 LEADS 100W
KT 3146 1 SCREW 30W 0.02A 1A SEE FIG. 4, D
KT 3126 0.1 SCREW 30W 0.2A 10A SEE FIG. 4, D
KT 3130 0.01 SCREW 30W 1A 50A SEE FIG. 4, D
KT 3131 0.001 SCREW 30W 2A 100A SEE FIG. 4, D
(1)
A suitable heatsink must be provided, See “INSTALLATION” paragraph.
Power Rating based on 275 °C max. hot spot temperature in 25 °C ambient, derate to 80% power in 71 °C ambient.
(2)
These sensing resistors are designed to provide a 0-200mV sample voltage for currents of 20A (KT 2713) and 200A (KT 2714) respectively.
RESISTANCE
(OHMS)
TERMINATION
POWER
RATING
RECOMMENDED OUTPUT CURRENT RANGE
(1)
BASED ON 1-VOLT SAMPLE
LOW HIGH
(2)
N.A.
(2)
N.A.
N.A.
N.A.
(2)
(2)
OUTLINE
DIMENSIONS
SEE FIG. 4, A
SEE FIG. 4, B
KEPCO, INC. " 131-38 SANFORD AVENUE " FLUSHING, NY. 11355 U.S.A. " TEL (718) 461-7000 " FAX (718) 767-1102
©2007, KEPCO, INC 1
Data subject to change without notice 228-0949 REV 6
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SENSING RESISTOR SELECTION
The value of the sensing resistor (R
sample is provided at the maximum output current (l
) is selected according to the desired output current range, such that a I-volt
S
1 Volt
R
--------------------= (See Table 1 for values.)
S
IOMax.
MAX):
O
INSTALLATION
The minimum required heat sink area for the listed power rating of the current sensing resistors is 144 square
inch, 1/4 in. thick aluminum (950 square centimeters, 0.5 centimeters thick). If the actual power dissipation
(MAXIMUM OUTPUT CURRENT TIMES ONE VOLT) exceeds one-tenth of the power rating, additional
cooling by means of an air stream or an oil-bath should be provided to keep the heat-rise in the sensing
resistor to a minimum. To minimize output ripple (“pick-up”) mount the sensing resistor assembly as close to
the power supply as practicable. Use shielded cable to connect the current control resistor to the null junction of
the power supply and connect the shield (single-ended) to the common signal ground.
INTERCONNECTIONS
The simplified connecting diagram (refer to FIG. 2) shows the electrical connection of the Sensing and Control
Resistors to a typical Kepco Power Supply. The nomenclature used in the diagram coincides with that used on all
Kepco Power Supplies. Refer to your Kepco Instruction Manual when in doubt about interconnections or terminal
designations.
NOTE: If the load must be protected from excessive compliance (output) voltage, a zener diode, rated to
conduct at the desired voltage, should be connected as shown in FIG. 2.
NOTE:
RS should be physically located as
close to the (+) output terminal of the
power supply as possible. In this
case, the link (+) OUT – (+) SENSE
CAN BE CLOSED and the connection (+) SENSE to terminal P of R
can be deleted. If RS must be
located some distance from the
power supply, the sensing connection as shown must be used (link
(+) OUT – (+) SENSE removed) and
the (+) terminal of the output capacitor (C
must be internally recon-
O
nected from the (+) sensing to the
(+) output terminal.
S
FIGURE 2. EXTERNAL CURRENT SENSING AND CONTROL USING THE VOLTAGE MODE AMPLIFIER
KEPCO, INC. " 131-38 SANFORD AVENUE " FLUSHING, NY. 11355 U.S.A. " TEL (718) 461-7000 " FAX (718) 767-1102
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2 228-0949 REV 6 083107
CALIBRATION PROCEDURE
The Kepco power supply, now converted to supply stabilized output current, can be calibrated by means of its built-in
I
CAL and Eio ZERO controls and by adding a precision ammeter (or a voltmeter parallel to the sensing resistor) in
b
series with the load. If the power supply lacks the calibration controls, they may be added externally to most Kepco
power supplies. (Refer to your Kepco Instruction Manual). Connect the load, the calibrating instrument and the external components as shown in FIG. 3. Proceed as follows:
1. Turn calibration set-up “on” and allow for a sufficient warm-up period. (Warm-up time depends on the environmental temperature, the power supply output power and the effectiveness of the heat-sink on which the
external sensing resistor is mounted.)
2. Turn the external current control resistor (R
selected range. Set (R
) to “zero ohms” (CCW).
CC
3. Observe the calibrating meter (M1). Correct zero point by adjusting the built-in (or external) E
trol.
4. Turn (R
adjusting the built-in (or external) I
) to its maximum resistance position (CW). Observe M1. Correct maximum output current point by
CC
CAL control.
b
) through its range to check for smooth operation over the
CC
ZERO con-
io
5. Recheck “zero” point by repeating procedure described in steps 2 and 3 above.
NOTE: The limitation imposed by using a single sensing resistor and by parallel leakage paths inside the power
supply restrict the usable output current range, obtainable with the described method, to approximately
2% to 100% l
max. If current control over a wider range is desired, two or more ranges can be imple-
O
mented, each range requiring its own sensing resistor, calculated on the basis of a l-volt sensing voltage
at the maximum range current. For a power supply with a maximum rated output current of 50 amperes for
example, two sensing resistors (Model KT 1915 and Model KT 2330) would cover the ranges from 0.02
Ampere to 1 Ampere and from 1 Ampere to 50 Amperes. (See Table 1.)
.
NOTE:
RS should be physically located as
close to the (+) output terminal of the
power supply as possible. In this
case, the link (+) OUT – (+) SENSE
CAN BE CLOSED and the connection (+) SENSE to terminal P of R
can be deleted. If RS must be
located some distance from the
power supply, the sensing connection as shown must be used (link
(+) OUT – (+) SENSE removed) and
the (+) terminal of the output capacitor (C
must be internally recon-
O
nected from the (+) sensing to the
(+) output terminal.
S
FIGURE 3. CALIBRATION SET-UP
KEPCO, INC. " 131-38 SANFORD AVENUE " FLUSHING, NY. 11355 U.S.A. " TEL (718) 461-7000 " FAX (718) 767-1102
083107 228-0949 REV 6 3
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NOTE: Dimensions shown in parentheses are in millimeters.
A. TYPICAL 50W RESISTOR (LEADS)
B. TYPICAL 100W RESISTOR (LEADS)
MOUNTING HARDWARE
SCREW, 4-40 X 3/8 ST. BHPH (KEPCO P/N 101-0461)
WASHER, #4, FLAT LOCK, ST (KEPCO P/N 103-0063)
NUT, HEX, 4-40 X 1/4 ACF, ST., (KEPCO P/N 102-0003)
MOUNTING HARDWARE
SCREW, 4-40 X 1-1/4 ST. BHSL (KEPCO P/N 101-0089)
WASHER, #4, FLAT LOCK, ST (KEPCO P/N 103-0063)
NUT, HEX, 4-40 X 1/4 ACF, ST., (KEPCO P/N 102-0003)
C. KT 1304 CURRENT CONTROL RHEOSTAT
D. TYPICAL 30W RESISTOR (SCREWS)
MOUNTING HARDWARE
SCREW, 6-32 X 1/2 BR. BHPH (KEPCO P/N 101-0071)
WASHER, #6, INT LOCK, ST (KEPCO P/N 103-0015)
NUT, HEX, 6-32 X 1/4 ACF, ST., (KEPCO P/N 102-0004)
WIRING HARDWARE (SUPPLIED)
SCREW, M4 X 8MM, SS. PHPH (KEPCO P/N 101-0463)
WASHER, #6, FLAT LOCK, ST (KEPCO P/N 103-0028)
NUT, HEX, 6-32 X 1/4 ACF, ST., (KEPCO P/N 102-0004)
FIGURE 4. MECHANICAL OUTLINE DIMENSIONS
KEPCO, INC. " 131-38 SANFORD AVENUE " FLUSHING, NY. 11355 U.S.A. " TEL (718) 461-7000 " FAX (718) 767-1102
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