The 701 Series of current sensing coils represents a quantum leap in the price and performance for resistance welding and other current measurement applications! They have the lowest position sensitivity of any fixed or flexible coil available today. These coils are intended for use with weld controls or as an upgrade coil for resistance welding current monitors. This series of coils is extremely rugged in design and construction for the most demanding applications environmental requirements. These coils have extremely low position sensitivity - approximately 5 times lower than coils presently available from other manufacturers. This makes concerns over their orientation in a welding loop a thing of the past. Other coils can change their readings up to 7% from their calibrated value, depending on their orientation in the welding current path. This amount of change makes the practice of calibrating a coil by a supplier and then relying on that same value after installation in welding equipment of little or no use.

Current sensing coils can be used in environments with widely varying temperatures. In some cases the current sensing coils can experience temperatures ranging from 40 °F to greater than 120 °F. HCT has measured the temperature sensitivity of many coils used in welding equipment. Temperature coefficients as high as ± 0.09%/°F have been found. If these coils are calibrated or specified at 70 °F it is possible to see false indications in measured current values based on:

%ERROR = TC D T

where

TC is the temperature coefficient of the coil in units of %/° , and

D T is the change in temperature from the reference or calibration/adjustment temperature

For example if the weld (or other current-related process) is developed at 70 ° F and the temperature during your production increased to 120 ° F your indicated current will change or be in error by 4.5%!!!! Further, you will not know this error is effecting your process!

Currents produced by modern SCR weld controls are not sinusoidal. Weld currents are made up of many frequencies- known as harmonics. A coil must be able to accurately process frequencies up to at least 1000 Hz to properly measure or control weld current. A measure of how well the coil measures a range of frequencies present in complex currents is its phase error over a range of frequencies. The 701 series of coils improves errors due to phase by a factor of 5 over other coils presently available.

Every 701 series coil comes with a certified value of mutual inductance accurate to ± 0.1% and actual position sensitivity test results. All certificates meet the most stringent quality system requirements. Testing meets or exceeds the new testing per American Welding Society Draft Standard A10.C Specification for Calibration and Performance Testing of Secondary Current Sensing Coils and Weld Current Monitors used in Single Phase AC Resistance Welding.