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Frequently Asked Questions
• Is Isotek the manufacturer?
• Who is ISABELLENHÜTTE?
• What does ISA-PLAN® mean?
• In my current sensing application, I expect a high current pulse at the beginning of each cycle. What level of inrush can your ISA-PLAN resistor handle?
• My circuit will require a 10 milliohm resistor for precision current sensing. Will I need a four terminal (Kelvin) resistor, or would a two terminal be okay?
• I plan on using two Kelvin resistors in parallel. How do I combine the sense voltage to determine the precise amount of current flowing through both resistors?
| Q. | Is Isotek the manufacturer? |
| A. | Isotek is a subsidiary of Isabellenhütte and does manufacture some items, such as the Voltmeter Current Shunts. However, for RARA high power metal clad resistors we are the sole agent. |
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| Q. | Who is ISABELLENHÜTTE? |
| A. | ISABELLENHÜTTE is a vertically integrated manufacturer of resistance alloys, thermo electric alloys, precision current resistors and precision measurement systems and therefore controls all stages of the manufacturing process from smelting the alloys to testing the finished resistors and systems. ISABELLENHÜTTE is certified ISO 9001 (QS 9000 in process)and manages a calibration lab under the auspices of the German Calibration Service (DKD - Deutscher Kalibrierdienst) which is subject to supervision by the national bureau of standards (Physikalisch-Technische Bundesanstalt_PTB). |
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| Q. | What does ISA-PLAN® mean? |
| A. | ISA-PLAN is a technology developed by ISABELLENHÜTTE, Heusler, GmbH KG of Dillenburg, Germany. This technology consists an etched manganin foil resistor element laminated to an aluminum or copper substrate with an electrically isolating but thermally conductive adhesive. The special manufacturing process and mass production techniques are also part of this advanced technology. |
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| Q. | In my current sensing application, I expect a high current pulse at the beginning of each cycle. What level of inrush can your ISA-PLAN resistor handle? |
| A. | The unique laminated construction of ISA-PLAN increases the effective thermal mass of the resistance element. Therefore, a factor of ten (10) times the continuous power rating is acceptable for pulses up to one second in duration. This factor varies somewhat with the specific resistor package and the duty cycle of the pulse. |
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| Q. | My circuit will require a 10 milliohm resistor for precision current sensing. Will I need a four terminal (Kelvin) resistor, or would a two terminal be okay? |
| A. | Kelvin connections are recommended for precision low-ohmic current sensing applications. The tcr of copper is 4000ppm/°C as compared to 10ppm/°C of Manganin. So in a two terminal resistor, this error is in series with the 10 milliohm resistor and could produce a significant variation in effective resistance as the temperature of the resistor changes. We recommend Kelvin connections whenever using 80 milliohm or less resistors. |
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| Q. | I plan on using two Kelvin resistors in parallel. How do I combine the sense voltage to determine the precise amount of current flowing through both resistors? |
| A. | When routing the sense voltage to the high impedance meter, a resistor equal to 1,000 times the sense resistor value should be put in series with each positive and negative sense lead (10 milliohm sense using two 5 milliohm resistors in parallel would require a 5 ohm resistor in series with each of the four sense lines). |
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