Resistors for very high accuracy
Guide for Precision Resistors
What is a precision resistor?
Measuring resistors are ohmic resistors which have to meet the particularly high requirements of precision measurement technology. Therefore, they are precision resistors without exception. They are used for current and voltage measurement and are usually used in voltage divider circuits. Because of their precise, stable resistance value, currents can be measured accurately if the voltage is known exactly (and vice versa). Depending on the application, different types of precision resistors are suitable for this task. Among them are special power resistors and shunt resistors, which are suitable for applications with high voltages and/or currents. The design can be very different and the term measurement resistor is used when the application is about solving a measurement task.
Tips for precision resistors
The range of measuring resistors and the application field are so broad that a simple statement about which resistor is suitable and when cannot be answered in a generalized way. One can generalize the technological characteristics due to the respective design.
Due to their design, measuring resistors with resistive elements made of wire (i.e. wirewound resistors) have an inductance that limits their use at high frequencies. Special winding procedures are used here to attempt to reduce this effect significantly at the relevant frequencies in the application. They offer the best possibility to achieve an exact resistance value with very good resistance tolerances. This advantage is therefore especially useful when a special value of the total resistance has to be achieved which is not available as standard product. However, if this is not required, metal foil and metal film resistors are usually the better choice today because they do not have these frequency effects. However, on the one hand the working temperature range is limited compared to wire elements and not all of them are suitable for higher power consumption.
Features of a precision resistor
Simply put, a precision resistor is a "more accurate" resistor compared to conventional products that are available in bulk. In addition to the generally higher quality requirements, the following main characteristics are decisive for the use of the term "precision resistor", depending on the design, in order to distinguish these resistors from "standard goods" or "mass-produced goods":
- Much tighter resistance tolerances
- Production of precise resistance values according to requirements / function
- Lower temperature coefficient (TK value)
- Far better long-term behaviour
- Larger special temperature ranges (partly up to 300 °C)
- Reduced current noise
- Suppression of inductance and/or capacitance effects
- Special housings / connections Four-wire or Kelvin measuring method
Depending on the technology and method, the better tolerance is achieved by material selection or by selection. The temperature coefficient, on the other hand, is a material property throughout. A better long-term behaviour is achieved by using high-quality materials and by artificial ageing or preloading.
|Example NC550 @ 100 kΩ||Conventional carbon film resistor "Noname" @100 kΩ|
|Temperature coefficient TC||±3 ppm / °C||-700 up to 0 ppm / °C|
|Technology / Material||Metal film / NiCr alloy||Carbon layer|
The table shows a comparison of a precision wirewound resistor of our product range with a conventional, comparable carbon film resistor.
Precision resistor types
In our portfolio for resistors you will find exclusively fixed resistors. This means that our resistors are selected according to a fixed ohmic value. Variable resistors, if you like, can be found in our portfolio for potentiometers. However, we recommend not to use these products as variable resistors.
Basically all our resistors are precision resistors due to their quality, function and performance, and are suitable for many applications. The narrow resistance tolerances, precisely selectable ohmic values, as well as the stability and long-term behaviour clearly differentiate them from standard resistors.
We offer fixed resistors in the following technologies:
- Wirewound resistors
- Metal film resistors
- Metal foil resistors
- Full metal resistors
Wired resistor with an extremely wide resistance range of 0.01 Ω...6 MΩ, tolerance up to ±0.005% and a maximum working voltage of 900V.
Radially wired resistor with wide resistance range of 0.01 Ω...1 MΩ and tolerance up to ±0.005%.
Metal film resistor with wide resistance range of 1 Ω…5 MΩ and resistance tolerance up to ±0.05%
Radially wired resistor with resistance range of 10 Ω...1 MΩ, resistance tolerance up to ±0.01% and max. working voltage of 500V.
Ultra-precise zero-TCR-resistor with resistance tolerance up to ±0.005% in metal housing
Measuring resistors are used as "normal" in applications for current and voltage measurement. Due to their purpose, measuring resistors are therefore basically precision resistors and must have very high accuracy. With peak values of up to ±0.005% in resistance tolerance and a temperature coefficient from < ±1 ppm/°C, these ultra-precise measuring resistors are designed for high-precision instrument construction.
Crosswise through almost all resistor technologies precision resistors can be manufactured as power resistor, voltage divider, shunt or SMD with the required accuracy. Precision resistors are very often individual components and exactly tailored to the needs of the application.
Within the scope of our "Resistor Engineering" we advise you on the best functional and economical solution. With assured quality products and high delivery reliability, we focus on long-term partnerships and accompany you throughout the entire life of your application.