Do you have over-voltage surge problem?

Written by riedon Saturday, 14 January 2012 03:17

Wirewound resistors, ideal at handling overvoltage surges, are often specified for the surge and overload conditions of harsh environments. The core of a wirewound resistor typically consists of fiberglass or a ceramic rod, with metallic wire wrapped around the substrate. While ceramic is more expensive, it acts as a heat sink and provides for an increase in efficiency as the surge event lengthens, whereas fiberglass provides little thermal benefit in overload situations.

There are several ways to increase the surge capability of a wirewound resistor. First, carefully selected longer lengths of larger diameter (lower resistance) wire can be tightly wound on the substrate. This leads to an increased resistance element mass. Additionally, the surge capability can be increased by using two layers of wire and winding them in opposite directions to reduce the resistor’s inductance. Not only does this decrease the inductance, but it also increases the resistance wire mass, which in turn improves the resistor’s surge handling capability.

For another article about resistors and over-voltage issues click here.

Resistor Technology Comparison

Written by riedon Friday, 13 January 2012 10:50

Termination Resistors for 4-20 mA Industrial Instrumentation

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:

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