In a recent conversation with my product manager I was provided a list of questions that Riedon is frequently asked about their shunts. Below is the list of questions the answers that Riedon has provided.
What is a shunt?A shunt is simply a very precise resistor with its general operation adhering to Ohm’s law.
What is a Current Shunt Resistor?
Current shunt resistors are a low resistance precision resistor used to measure AC or DC electrical currents by the voltage drop those currents create across the resistance. These are also sometimes called ammeter shunts , which are a type of current sensor.
What is the best way to mount a shunt?Ideally, shunts should be mounted such that the resistive elements are oriented in a vertical plane to promote better cooling of the elements. This means that our shunts that include a base should be mounted to a panel or wall and not a floor or ceiling.
What is the accuracy of Riedon shunts?We offer a standard tolerance of ±0.25%, however, we may be able to provide shunts with a tolerance as tight as ±0.1% on request.
What voltage output options are offered for your shunts?Our shunts are offered with either 50mV or 100mV outputs as standard. However, we can support nearly any voltage output on request including 60mV and 75mV.
Are your shunts MIL spec?The MK series of shunts are built to meet the standards of CID (commercial item description) A-A-55524, which superseded MIL STD 91586
What does rated current mean in regards to your shunts?Our shunts are offered in many standard current ratings. This rating, often referred to as full scale, when applied to the shunt will result in the selected voltage output. For continuous use, we recommend that the shunt be operated at no more than ⅔ rated or full-scale current.
Why do you recommend de-rating your shunts by rated or full-scale current?We recommend not exceeding ⅔ rated or full-scale current in order to limit thermal heating of the resistive element.
What is the power rating for your shunts?The power rating of a shunt will always adhere to Ohm’s law and may be calculated using the formula P=I*V, where I is the rated current and V is the chosen milli-volt output of the shunt.
Can shunts be used to measure short duration pulses?Yes, a shunt can be used to measure pulses. There is an important thing to keep in mind, however. It is permissible to exceed the rated current of a shunt for a short period of time. The length of time will depend entirely on thermal concerns. It is important that the resistance element of the shunt not exceed 140°C or the resistance value will forever be altered and the shunt ruined. In order to provide an additional safety factor, we recommend that the temperature of the resistance element not exceed 125° C. Keep in mind that the voltage output of the shunt will be proportional to the input current, so it is necessary to ensure that the input of any monitoring equipment not be exceeded.
Can shunts be used to measure AC currents as well as DC currents?Riedon shunts may be used to measure low frequency AC currents. There is the possibility of electrical noise at higher frequencies, however, experience shows that the shunt will behave very well at frequencies up to about 1kHz.
Do you provide calibration certificates for your precision shunts?We can provide documentation confirming the results of calibration. We calibrate all of our shunts using NIST traceable components.
I’d like to monitor a 500-watt source, will your shunts do this?Probably! Remember that the shunt is not measuring the power of the source, only the current it provides to the load. Determine the expected current draw and then divide the expected current draw by ⅔ or 0.666 to determine the full scale or rated current you will need. You will also need to decide if you would prefer a 50mV or 100mV output.
What is the operating temperature range of your shunts?Our shunts will be most accurate when operated at temperatures between 30° C and 60° C. Below that temperature the shunt will not sustain any damage, but its accuracy will not be as precise. The absolute maximum temperature of the resistive element is 145° C. Any temperature above that will permanently damage the shunt. We recommend not exceeding 125° C to allow for a margin of safety.
Do you offer customization services for your shunts?Absolutely! We have helped design and have manufactured a number of application specific models for use in everything from electric vehicles to aerospace. We welcome both customer specific drawings as well as modifications to our standard shunts.
What are the recommended wiring guidelines for your current sensing shunts?Shunts should be wired into the circuit to be monitored in the ground or return line as close as practical to the power source. This will limit the voltage differential between the terminals of the shunt and ground, thus providing a degree of safety against electrical shock. In addition, placing the shunt near the power source will ensure that all of the loads are accounted for.
Is ±0.25% the best tolerance you offer for your shunts?±0.25% is our standard tolerance, however, a large portion of our shunts are available with tolerances as tight as ±0.1%. Please send us an inquiry and we will confirm availability of the tighter tolerance.
Question: What is the TCR (temperature coefficient of resistance) of your shunts?
Answer: Our shunts utilize a manganin resistive element that features a very stable TCR of 15ppm to 20ppm in a temperature range of 30° C to 60° C.