RSN Series – Riedon™ DC Ammeter Shunts / Busbar Shunts by Bourns

Shunt FAQs

Question: What is a shunt?

Answer: A shunt is simply a very precise resistor with its general

operation adhering to Ohm’s law.

Question: What is a Current Shunt Resistor?

Answer: 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.

Question: What is the best way to mount a shunt?

Answer: 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.

Question: What is the current lead time for your shunts?

Answer: Many of our shunts and fuse blocks are available from

stock. If the device you are seeking is not in stock, our current

manufacturing lead time for new orders is four to five weeks,

often sooner.

Question: What is the accuracy of Bourns® shunts?

Answer: 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.

Question: What voltage output options are offered for your

shunts?

Answer: Our shunts are offered with either 50 mV or 100 mV

outputs as standard. However, we can support nearly any

voltage output on request including 60 mV and 75 mV.

Question: Are your shunts MIL spec?

Answer: The MK series of shunts are built to meet the standards

of CID (commercial item description) A-A-55524, which

superseded MIL STD 91586.

Question: What does rated current mean in regards to your

shunts?

Answer: 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 2/3 rated or full-scale current.

Question: Why do you recommend de-rating your shunts by

rated or full-scale current?

Answer: We recommend not exceeding 2/3 rated or full-scale

current in order to limit thermal heating of the resistive element.

Question: What is the power rating for your shunts?

Answer: 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.

Question: Can shunts be used to measure short duration

pulses?

Answer: 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.

Question: Can shunts be used to measure AC currents as

well as DC currents?

Answer: Bourns 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 1 kHz.

Question: I’d like to monitor a 500-watt source, will your

shunts do this?

Answer: 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 2/3 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 50 mV or 100 mV output.

Question: What is the operating temperature range of your

shunts?

Answer: 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 140 °C. Any temperature above that will

permanently damage the shunt. We recommend not exceeding

125 °C to allow for a margin of safety.

Specifications are subject to change without notice.

Users should verify actual device performance in their specific applications.

The products described herein and this document are subject to specific legal disclaimers as set forth on the last page of this document, and at www.bourns.com/docs/legal/disclaimer.pdf.