Termination Resistors for 4-20 mA Industrial Instrumentation

Last Updated on Tuesday, 10 January 2012 03:28 Written by Frieda Thursday, 12 January 2012 02:32

Modern industrial automation applications demand high performance instrumentation.  A well-established technique is to use 4-to-20 mA current-mode transmission (rather than voltage signal) between process sensors and data-processing system elements.  This method is less susceptible to the electrical noise problems common in industrial automation and control system applications.

However, modern data-processing components are typically designed for voltage inputs, especially those based on digital technology.  The 4-20 mA signals from remote sensors must be converted to voltage level signals, typically 0 to 5 volts, for compatibility with these components.

This conversion is relatively simple requiring only a resistor (Figure 1).  Obviously, the accuracy of the current-to-voltage conversion depends upon the precision of the resistor.  Riedon precision resistors are ideal for this application:

Continue here

Why Buy Matched Set Resistors?

Last Updated on Friday, 18 March 2011 12:09 Written by Frieda Wednesday, 16 March 2011 04:11

Matched resistors are a set of resistors where an additional parameter(s) is given to link the resistors. For example, resistor ‘A’ and resistor ‘B’ have

matched resistors

a resistance of 100Ω, a tolerance of 5%, and a TCR of 25 + 5 ppm. You may add additional parameters to this set calling for the pair to be no more than 1% apart and also within 5ppm of each other. If resistor ‘A’ is 95Ω and resistor ‘B’ is 105Ω, both of which are within their individual tolerances, then these resistors would not be matched since they deviate more than 1% in comparison to each other. Conversely if resistor ‘A’ has a ppm of 20 while resistor ‘B’ has a ppm of 25, then the TCR of these resistors would be matched since they meet the requirement of being no more than 5ppm apart from each other. It is important to consider TCR as well due to the variation in resistance as the components heat up, which may flaw your design. This is not limited to only a pair of resistors and can be applied to as many as your application needs.

There are applications

where choosing matched resistors is sometimes necessary and advantageous financially. Take for example a simple voltage divider. If precision in the output voltage is important in your design then choosing a set of matched resistors is crucial. You may be wondering why you wouldn’t select some precision resistors for your design instead and you wouldn’t be wrong in assuming so. However in applications where the ratio of the resistors is more important thanthe precision of the resistors, it would cost less to purchase a set of resistors with a tolerance of 1% matched to 0.1% than to produce a set of resistors with a tolerance of 0.1%.

Some industries of interest are oil and gas in their use of down-hole instruments and various military applications and scale instrumentation. If you are unsure whether or not you are able to apply matched resistors in your application, please do not hesitate to ask Riedon. With over x years of experience in producing custom resistors, we are confident in our ability to assist you in your design

Pulse Rated Resistors

Last Updated on Friday, 4 March 2011 10:56 Written by Frieda Thursday, 17 February 2011 07:56

The Riedon  “Pulse Rated Resistors”  training module is now available for customers to download from Digi-Key’s Web site.

Please go to  the Riedon supplier page on the Digikey site and click the link titled “Product Training Modules” .

It includes voice over training option,  so make sure  you  have the volume up and feel free to share this with customer who would be interested in  high pulse rated resistors.