Electronic – the difference between high precision resistors and current sense resistors

current measurementprecisionresistors

Actually, I am trying to build a current monitor for a wireless sensor network. I am going to use a current sense resistor as the current will pass through the resistor. By measuring the value of the voltage, the current value can be calculated.

My application is very sensitive as the current that will be measured is in the range of mA, 30 mA maximum.

When it came to buying the resistors I got confused. I found a type of resistor called "precision resistor" that has a very small error, and another one called "current sense resistor".

Here is a picture of a current sense resistor:

current sense resistor, 25 ohm, 1%

So my questions are:

  1. What is the difference between these two types current sense and precision resistors?
  2. How does this current sense resistor differ from the ones we normally use, such as as these 5.6k Ohm, 5% resistors?

4x 5.6k Ohm 5% resistors, image source wiseGEEK

Best Answer

Resistors are resistors. They only see the current thru them and the voltage across them.

However, specific models can be targeted to specific applications. What you show as a current sense resistor looks like it's designed to dissipate significant power. However, it would work for lots of purposes within its power and voltage limits.

Current sense resistors tend to:

  1. Be run with little voltage across them.

  2. Be fairly accurate, since being used for measurement.

  3. Drift little due to temperature.

  4. Have low values.

  5. Sometimes have 4 leads so that you can use a Kelvin connection. Two leads carry the current, then the voltage is measured across the two other leads. This keeps the voltage drop due to current in the leads off the measurement.

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