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Details, datasheet, quote on part number:39-1734102
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DMS Accessories
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POINTS TO KEEP IN MIND WHEN YOU USE A DC AMMETER SHUNT
These shunts are designed for use with 50 or 100 millivolt measuring instruments, calibrated in terms of the ampere ratings of the shunt. The accuracy of these shunts is better than ±1/4% of the rated value and the temperature coefficient is ±0.000015. It is important that the resistance be constant under different temperature conditions. It is usually assumed that the maximum temperature will be about 80°C and the usual range is 40° to +60°C. For continuous operation, it is recommended that shunts are not run at more than two-thirds (2/3) the rated current under normal conditions of use as per IEEE standards. If the shunt is used in an AC or pulse current environment make sure that the highest pulse current will not exceed the recommended two-thirds, the rated current for continuous operation. In this case, the average millivolt reading using an rms meter will be proportional with the duty cycle of the AC current. 1.0 INSTALLATION By definition, a shunt is a resistor, and will generate heat with passage of current. Because of this, the resistance blades of the shunt should be mounted in a vertical position to promote free convectional flow of air. Where this mounting position is impractical and in installations where the shunt is in a confined location, forced air cooling should be provided. Under no condition should the manganin shunt strip be allowed to surpass 145°C, as this will cause a permanent change in resistance. Shunts should be installed to protect them from damage by thermal expansion forces in the connecting bus bars or by short circuit forces. It should be recognized that shunts are inherently weaker than their current connections and that special flexibility may be needed at times. Where possible all shunts should be connected in the grounded side of the line. See Figures 1 and 2. Portable type shunts, with an insulating base, when used on circuits above 750 volts should be mounted in the grounded side of the circuit. Where more than one bus bar is to be connected to each end of a single terminal shunt, these bars should be distributed as equally as possible on each side of the shunt terminals. 2.0 SHUNT SELECTION GUIDE Selection of ratings should be based on operation at a normal current of 2/3 the rated value. Ratings are based on mountings in accordance with Reference Test Conditions: · Reference Temperature: 25°C (±2°C) · Position: Current terminals and resistance blades, vertical, allowing free air circulation. · Connections: Tightly bolted to current bus using all terminal slots and specified depth of blade insertion or tightly bolted to lugs with cables or proper crosssection. Since a shunt is essentially part of a bus-bar assembly, it depends on the structure to conduct away a major portion of the heat generated within the shunt and then to radiate this heat. It is important, therefore, that these connecting buses be of ample size and properly attached to the shunt. 3.0 DESIGN CONSIDERATIONS When trying to find the correct shunt rating to specify for a given application, there are four things to take into account: A. Duty continuous, intermittent or surge B. Ambient elevated temperature or high altitudes C. Temperature rise normal or limited D. Environment grouped, enclosed, forced air E. Combinations of A through D Although each of these conditions will be considered separately, any combination of them may exist in a specific case. When this happens it will be necessary to use more than one of the following sections to arrive at the correct rating. 4.0 DUTY For duty which is less than continuous, a shunt need not be rated as high as a straight calculation based on resistance and voltage or current would indicate. If, for instance the shunt is repeatedly energized for a short period (not to exceed 5 minutes)...a conservative rating may be obtained as follows:
4-Wire DC Current Shunts
5Vdc POWER SUPPLY
DC LOAD
DC LOAD Power Supply
DC LOAD
12
12 11
DC CURRENT SHUNT
12
Isola ted 5V dc Power
12 11
DC CURRENT SHUNT
7
84
3
7
84
3
DMS-20PC-0-RL
DMS-20PC-0-RL
Figure 1. Shunt connected on the low side with the meter powered from the same supply.
Figure 2. Shunt connected on the low side with the meter powered from an isolated power supply.
K1
D
where D is the ratio of ON time to the total period.
Ppuls = Pmax / K1 Pmax = Prated x 0.66 Pmax = maximum continuous power Prated = catalog rated power Ppuls = maximum pulsating power For surge and pulse service a different approach must be used. In these cases it is necessary to provide enough thermal mass to absorb the energy to be dissipated and be sure that the construction of the shunt is adequate to accommodate the peak power. Therefore, it is recommended that a complete description of the pulse/surge wave shape or circuit constants and operating conditions be submitted to DATEL for the selection of a suitable shunt. 5.0 AMBIENT If the ambient temperature of the area in which the shunt is to operate exceeds the ambient Reference Test Conditions, a derating factor must be applied to prevent the manganin temperature from going above the safe limit of 125°C. The following formula may be used to find the de-rating power. Pout = Pmax x (1-T/ A) Pmax = Prated x 0.66 where T is the difference between the rated and operating ambient temperatures, A is the rise allowed above the rated ambient and Pmax is the Pout at 25°C. Example: A 800 Amp 50mV shunt is energized for 15 seconds of each minute.
0.62"
DC CURRENT SHUNT DC LOAD Powe r Supply
12
Isolated 5Vdc Power
11 12
DC LOAD
7
84
3
DMS-20 PC-0-RL
Figure 3. Shunt connected on the high side with the meter powered from an isolated power supply.
Figure A
0.20" DIA 2 PLACES
1.25" 0.62"
0.50"
0.87" 0.43"
1.0" 2.0"
8-32 SCREW 2 PLACES
1/4-28 UNF STUD 1/4-28 UNF HEX JAM NUT
D = 15 / 60 = 0.25 and K1 0.25 = 0.5 thus, Prated = 800 x 0.05 = 40 watts Pmax = Prated x 0.66 = 40 x 0.66 = 26.4 watts Ppuls = Pmax / K1 = 26.40 / 0.5 = 52.8 watts therefore this shunt can be loaded up to 919 Amps.
Example: If a 150 Amp 50 mV shunt is to operate in a 100°C ambient, what is the maximum load? 100°C is 75 degrees above the ambient, so T = 75°C, and the rated rise A is 100°C. Figure B
1.68" 0.50"
0.56"
0.20" DIA 2 PLACES
Therefore: Pout = Pmax x (1-(75 / 100)) = Pmax x 0.25 Pmax = 0.66 x Prated = 0.66 x (150 x 0.05) = 4.95 watts Pout for an ambient of 100°C is Pout = 4.95 x 0.25 = 1.23 watts, 60 Amps will be the maximum load.
6.0 TEMPERATURE RISE In many cases it is desirable to limit the temperature rise of a shunt for increased accuracy and stability or to protect other equipment near it. A satisfactory derating factor "K2" may be obtained from:
0.62" 1.75" 0.62"
1.5" 3.25"
0.43" 0.75"
3/8-16 x 5/8 8-32 SCREW 2 PLACES
K2 = 1 - t / 125 where "t" is the difference between the rated and the newly imposed rise limit.
Example: Suppose it is necessary to limit the temperature rise of a shunt type LC800 Amp 50 mV to 75°C. What is the maximum safe load?
1.75"
0.562"
ORDERING INFORMATION Current Shunt 5A 50mV 50A 50mV 500A 50mV 10A 100mV 100A 100mV DATEL Part Number 39-1734102 39-1734101 39-1734109 39-1734119 39-1734120 Figure A A B A A
DS-0480B 2/02
t =125-75 =50 K2 =1 -(50 / 125) =0.6 Pmax = Prated x 0.66 =26.4 watts at 25°C K2 x Pmax = 26.4 x 0.6 = 15.84 watts; therefore 503 Amps represents the maximum safe load.
DATEL, Inc. 11 Cabot Boulevard, Mansfield, MA 02048-1151 Tel: (508) 339-3000 (800) 233-2765 Fax: (508) 339-6356 Internet: www.datel.com Email: sales@datel.com
DATEL (UK) LTD. Tadley, England Tel: (01256)-880444 DATEL S.A.R.L. Montigny Le Bretonneux, France Tel: 01-34-60-01-01 DATEL GmbH München, Germany Tel: 89-544334-0 DATEL KK Tokyo, Japan Tel: 3-3779-1031, Osaka Tel: 6-6354-2025
DATEL makes no representation that the use of its products in the circuits described herein, or the use of other technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained herein do not imply the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifications are subject to change without notice. The DATEL logo is a registered DATEL, Inc. trademark.
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