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.

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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Riedon fusible resistors are normally wire-wound resistor designed to open at power levels specified by the application.  These resistors must be specially analyzed and designed for a customer application in order to assure that the fuse opens under the right conditions and within the time duration specified by the application.

Please contact Riedon to discuss your fusing applications.  We would be happy to work with you to develop a product for your requirements.  Call us to get more information.

There are a number instances where energizing a circuit is followed by a surge of current. Like almost all the time. When that circuit “comes on” after the switch is flipped, current is flowing. And sometimes we need to place a resistor in series with the component or components that want to draw a ton of current on startup. We can look at a component that might just do that.

Capacitors (caps) are sometimes fitted with something that limits a big shot of current when a circuit is energized. Caps, you recall, begin operation in the circuit of a modern equipment uncharged, and when these caps are first “seen” by the voltage source at the moment it’s turned on, they look like a short circuit. Lots of current may want to flow. Jumping ahead, the cap sits in the operating circuit fat, dumb and happy “using” only a little current after things are going. But at startup, it needs to be checked to prevent it from “sucking up” (or sinking) too much current and overloading the supply. The surge resistor is on the job each time the circuit is energized.

There are other applications for a surge resistor, but the purpose is the same – prevent “too much current” from flowing at a given moment so the circuit can transition into a “normal operating mode” (where current flow is more modest).

The surge resistor is similar to a so-called current limiting (or, perhaps, ballast) resistor, but the name applied to the resistor in question might have more to do with the specific application. Wirewound resistors are perfect for high surge applications and Riedon offers one of the best “joule rated” resistors in the industry.

2)ULTRA LOW OHM CHIP In addition to the PCR series Riedon would like to introduce the CSR series, an Ultra-Low Ohm (Metal Strip) Chip Resistor. We are introducing this to meet the increasing demand in the market for low ohm surface mount shunts. This type of device is used across many industries and applications including DC/DC converters, chargers, or adaptors, and power management for battery charging. For more information on this resistor please click http://www.riedon.com/us/images/stories/pdf/CSR.pdf

3) HIGH VOLTAGE MELF During the continued success of our precision metal electrode leadless face resistors, the MFM series, Riedon has found the need for a MELF that can withstand high voltages. In order to meet this requirement we would like to introduce the MFM series, a high voltage MELF resists that is able to withstand an operating voltage up to 3000V. This is nearly 9X higher than the MFM series, which can withstand up to 350V. To find out more information about this resistors please click here http://www.riedon.com/us/images/stories/pdf/MGM.pdf

Resistors as Heaters

Power resistors and resistance heaters share many common design considerations. In both products, good thermal design ensures low thermal resistance between the element and the exterior environment. Both must be rugged and reliable.

Power resistors are often used in heater applications. They allow a designer to apply and control heat to a small area. Riedon offers a broad range of these resistors. If one of our standard resistors won’t do we can modify existing products or create new designs to fit your special requirements.

Riedon power resistors are used in a variety of heater applications. They are especially useful in situations where the heat must be isolated or concentrated in a small area.

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A surge resistor is a resistor installed in a circuit to prevent a “surge” when conditions arise where a surge might occur.

There are a number instances where energizing a circuit is followed by a surge of current. Like almost all the time. When that circuit “comes on” after the switch is flipped, current is flowing. And sometimes we need to place a resistor in series with the component or components that want to draw a ton of current on startup. We can look at a component that might just do that.

Capacitors (caps) are sometimes fitted with something that limits a big shot of current when a circuit is energized. Caps, you recall, begin operation in the circuit of a modern equipment uncharged, and when these caps are first “seen” by the voltage source at the moment it’s turned on, they look like a short circuit. Lots of current may want to flow. Jumping ahead, the cap sits in the operating circuit fat, dumb and happy “using” only a little current after things are going. But at startup, it needs to be checked to prevent it from “sucking up” (or sinking) too much current and overloading the supply. The surge resistor is on the job each time the circuit is energized.

There are other applications for a surge resistor, but the purpose is the same – prevent “too much current” from flowing at a given moment so the circuit can transition into a “normal operating mode” (where current flow is more modest).

The surge resistor is similar to a so-called current limiting (or, perhaps, ballast) resistor, but the name applied to the resistor in question might have more to do with the specific application. Wirewound resistors are perfect for high surge applications and Riedon offers one of the best “joule rated” resistors in the industry.

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High Voltage Resistors

APPLICATIONS/MARKETS FOR HIGH VOLTAGE RESISTORS:
MEDICAL : CAT Scan, Blood Analyzers, CO2 Lasers
OIL&GAS : Sensors, Off-Road Vehicles, Down-hole instrumentation.
INSTRUMENTATION: Microscope, Radiation detectors
DEFENSE: Radar, Satellite electronics, Remote instrumentation.

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