DMS Accessories www.murata-ps.com 50mV and 100mV Base-mounted DC Shunts Murata Power Solutions 50mV and 100mV base-mounted current shunts are designed for measuring dc currents from 5A to 1200A. These preci- sion shunts (+/0.25% accuracy) connect directly to MPSs DCA5-20PC Series of dc ammeters. Installation is straightforward: simply connect the load circuit to the shunts threaded studs and the shunts mV Kelvin- outputs to the digital ammeters input terminals. All models feature a rugged phenolic base that provides 750V isolation to the shunts brass terminals, allowing for direct attachment to metal surfaces. A highly stable (+/15ppm/C) manganin sensing-element provides a wide 40 to +60C operating temperature range. Please see the DCA5-20PC data sheet for additional ammeter-related information and detailed connection diagrams. To ensure that the manganin sensing element does not exceed 125C General Speci cations (All Models) under worst case operating conditions, please read and follow the guide- Rated Accuracy 0.25% max. lines in the mounting and derating sections of this data sheet. Tighten Sensing Element Manganin all connections on the shunt per the torque speci cations given in the mechanical dimensions and selection guide on page 3. Please note, the Terminal Posts/Screws Brass user is responsible for selecting the correct wire sizes (gauge) and wire Tightening Torgue See Mechanical Dimensions type for the given application. Current Rating See Selection Guide 2. Mounting Considerations: All shunts should be mounted with their resis- Operating Temperature 40 to + 60C (40 to +137F) tance blades in a vertical position to allow for natural convection cooling (see Figure 1). Forced-air cooling must be provided when vertical mounting is impractical, or in installations where the shunt is installed in a con ned Technical Notes location. The shunts manganin blades must never be allowed to exceed +125C doing so will cause permanent damage to the shunt. IMPORTANT To ensure safe and reliable operation, dc shunts and all associated equipment must be installed and serviced by quali ed Shunts must be installed in a manner that protects them from damage due technical personnel. Never make any connections to the shunt, the to thermal expansion forces produced by high- or short-circuit currents. In load, or the ammeter with energized power sources. Contact Murata most cases, shunts are weaker than their external-circuit connections, so Power Solutions if you have any questions regarding the installation provisions for additional wiring- exibility may be required in high current or operation of any of our instruments and accessories. and/or high-vibration applications. 1. Base-Mounted Shunt Precautions: DC current shunts are low value Whenever practical, all shunts should be connected in the grounded side resistors that develop a mV output when current passes through their (normally the chassis) of the dc supply. However, these shunts must be highly-stable manganin resistive element. Under high current, contin- connected in the grounded side of the circuit when the dc supply exceeds uous use operation, dc shunts will dissipate considerable power and 750 volts (the rated limit for the shunts phenolic insulating base). When may undergo a signi cant temperature rise. For example, if allowed more than one wire is to be connected to each end of a shunt, the wires to operate continuously at its full rated load, a 500A/50mV shunt must be evenly distributed between both terminals (see Figure 1). dissipates 25 Watts (500A x 0.050V = 25 Watts). Therefore, whenever Mount shunt on a vertical surface possible, be sure to specify 50mV shunts due to their inherently lower power dissipation and voltage drop. 50A 50mV LOAD CURRENT 50mV OUTPUT For full details go to www.murata-ps.com/rohs Figure 1. Typical installation www.murata-ps.com/support MPM DMS Accessories.D01 Page 1 of 4DMS Accessories 50mV and 100mV Base-mounted DC Shunts 3. Lead Extensions: The shunts Kelvin outputs (i.e., their 50mV or 100mV The following formulas can be used to calculate the maximum pulsed- output signal) should not exceed 24 inches in length (61cm), assuming current (Ipuls) for a given shunt: 22AWG (0.5mm2) wire is used. If longer leads are necessary, the Ipuls = Ppuls/R, and Ppuls = Pa/K1, and K1 = D additional voltage drops in the leads must be taken into consideration Where as they will degrade accuracy and stability. However, MPSs DCA5 series dcammeters feature a calibration potentiometer that can be used to Ipuls = Maximum pulsed current compensate for some additional losses when long leads are employed Ppuls = Maximum pulsed power contact MPS for calibration information. Pa = 0.667 x shunts rated power at 25C ambient 4. Continuous-Operation Derating: If continuous operation is required, D = Ratio of ON TIME to ON TIME + OFF TIME a shunt must only be allowed to carry 2/3 of its maximum nameplate (period not to exceed 5 minutes) amperage. The 2/3 derating factor provides an adequate safety margin for convection cooled shunts operating in an ambient temperature of K1 = Pulsed-operation rating factor (the square root of D) +25C. The following two sections contain additional derating that is R = Shunts resistance (see selection guide for values) required when shunts will be exposed to higher operating temperatures or pulsed (intermittent) currents. Example: An 800 Amp 50mV shunt will be operated for 15 seconds each minute. What is the maximum current this shunt can carry 5. Temperature Derating: If the shunt is to be operated at ambient during the 15-second ON time temperatures above +25C, the maximum continuous current must be further derated from the 2/3 value previously noted. To nd the maximum permissible continuous current (Ie) at an elevated K1 = D = 15/60 = 0.25 and = 0.50.25 temperature (Te), one must rst calculate the maximum allowable Pa = 0.667 (800A x 0.050V) = 26.7 Watts power dissipation (Pe) at Te, using the following formulas: Ppuls = Pa/K1= 26.7W/0.5 = 53.4 Watts Pe Pe = Pa x 1-(Te-25C)/100C , and Ie = R 53.4W = 924A Ipulsed = 0.0000625 Where Ie = Maximum permissible continuous current at elevated 0-50mV OUTPUT temperature Te Pe = Maximum power dissipation at the elevated temperature Te + R = Shunts resistance (see selection guide for values) Pa = 0.667 x shunts rated power at 25C ambient + + LOAD DC SUPPLY Te = Elevated temperature 50mV SHUNT Example: How much current can a 150 Amp 50mV shunt safely carry at an ambient temperature of +100C LOAD CURRENT POWER Te = +100C GROUND (0Vdc) Pa = 0.667(150A x 0.050V) = 5.0 Watts Pe = 5.0W 1-(100-25)/100 = 5.0W x (1-0.75) = 1.25W R = 0.00033 Ohms Figure 2. Typical Low-Side Shunt Connections Pe Ie = R Lastly, use the formula to nd the maximum derated 0-50mV OUTPUT continuous-current at Te = +100C: + 1.25W = 61.5A Ie = 0.00033 + DC SUPPLY 6. Intermittent (Pulsed) Operation: Shunts that will not be exposed to continuous operation at 2/3 rated current can be operated at levels 50mV SHUNT close to, oreven above, their nameplate ratings for portions of short periods of times (5 minutes maximum) at 25C ambient. LOAD CURRENT POWER GROUND (0Vdc) + LOAD Figure 3. Typical High-Side Shunt Connections www.murata-ps.com/support MPM DMS Accessories.D01 Page 2 of 4