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Saturday, 31 July 2010

Resistance Measurement

Resistance Measurement from Cropico

Automotive Resistance Measurement

Within the range, model 4001 also includes temperature compensation, with preset coefficients for copper and aluminium plus user settable coefficients for other materials. Temperature measurement over the range –50 to +800ºC is also available.

Protection up to 415V rms is provided at the measurement terminals and push button operation is achieved easily by clearly marked function controls. Direct reading measured values are displayed on a four-digit LCD display. Over range and low battery indication is also provided and warning LEDs illuminate when an open circuit lead condition is detected.

The versatile, rugged and easy-to-use (Digital Ohmmeter) D07Plus simplifies the resistance associated with electrical connections, weld integrity, cable and joint resistance, electric motors and other engineering applications.

Accurate to within 0.05%, lead resistance errors are eliminated with the incorporation of true four-wire technology, while advanced features include seven selectable measurement ranges, extending from 0.1μΩ to 6 kΩ - in addition to a 10A measuring current.

The D07Plus is capable of recording and storing 1,000 measurements plus sequences. There is an option for selecting continuous or pulsed current output.

A long scale count meter (up to 60,000) enables the automatic averaging of forward and reverse measurements, which can then be downloaded to a PC or printer if required via a full serial RS232 or USB outlet port.

Friday, 30 July 2010

Resistance & Temperature Measurement

Resistance & Temperature Measurement from Cropico

There are several reasons why the resistance of material needs to be measured in the automotive industry, particularly measuring the resistance of electrically powered equipment like robot welding cables to ensure the weld quality does not deteriorate.

Others include the measurement of battery lead crimp connectors, the resistance of air bag detonator, resistance of wiring harnesses and the quality of crimp connectors on components.

The ability to make accurate and reliable measurements is therefore crucial but, with the values involved usually very low - often down to milliohms - the key requirement is to understand and eliminate potential sources of error from the measurement process.

To achieve this Cropico, the specialist supplier of precision measurement equipment, offers a range of advanced, precision instruments capable of meeting the demanding requirements of the automotive production environment.

The Cropico Series 4000 digital ohmmeter range provides a practical solution for a wide range of low resistance measurement applications.

The portable and rugged instrument includes a number of advanced features to ensure measurement accuracy including forward and reverse current measurement with auto averaging, true current zero, long scale length and a selectable measurement range from 40mohms to 4k ohm with respective resolutions between 10m ohm and 1ohm.

Thursday, 15 July 2010

Temperature Measurement - Processes

Temperature affects all processes but it’s always difficult to measure. Here, Bill Earlie of electrical test and measurement specialists Cropico looks at one way of achieving greater accuracy in temperature measurement - platinum resistance thermometers.

Platinum resistance thermometers are much more accurate than thermocouples but they have some drawbacks, notably a more limited temperature range, a higher thermal mass and usually are more expensive. These resistance thermometers have a linear and repeatable resistance against temperature: The two common types in use are Pt100 which has a resistance of 100Ω at 0°C and Pt25 which has a resistance of 25Ω at 0°C.

Platinum is used because it has a stable temperature coefficient and being a noble metal is not very susceptible to contamination. Pt100 (PRT) is the most commonly used and has a temperature coefficient of ? = 0.00385 (European standard) which corresponds to an average resistance change, over the temperature range 0 to 100°C of 0.385Ω per °C.

Both the absolute resistance value and the change in resistance per °C are both relatively small and give rise to measurement problems, especially when the resistance of the connection leads are taken into consideration. There are other standards also in use – for instance, the US standard for pt100 has an alpha of 0.00392.

Thursday, 8 July 2010

Temperature Scales

There are three temperature scales in use today.
These are used for temperature measurement.

The Celsius scale, the Kelvin scale & the Fahrenheit scale. A comparison of the three can be found below:

Tuesday, 6 July 2010

What is Temperature?

Temperature can be defined as the amount of hotness or coldness of a body or environment.

It can, however, be more accurately described as molecular motion and energy flow, and can be measure in a number of ways ie. the expansion of a liquid as seen in liquid in glass thermometers, or the change in resistance of a material such as copper or platinum.

Cropico are world leaders in accurate temperature measurement.


Heat is internal energy that flows from a system at a higher temperature to a system at a lower temperature. Two bodies at the same temperature are said to be in thermal equilibrium.

If a body at a higher temperature comes into contact with a body at lower temperature, heat will flow from the higher temperature to the lower one. If an ice cube is placed in a warm drink the heat from the drink will flow into the ice cube and melt it. The ice cube does not transfer its coldness to the drink, but of course the overall effect is for the drink to become slightly cooler.