Isabellenhütte USA has created a list of frequently asked questions (FAQ’s) where an array of topics are covered. If you do not find the answer to your question, please contact us.


Are you ISO certified?

Yes! Isabellenhütte USA, Isabellenhütte Heusler GmbH & Co. KG, and RARA Electronics are all ISO certified. You can find all the certs in our Support and Resource area.

Do you accept credit cards?

Yes, we accept all major credit cards.

Where are your parts produced?

Most of our products are manufactured in Germany. Others are manufactured in Asia. 

Can I set up an open account?

Along with your first order (min. $500 to establish an account), upon credit approval, we will extend Net 30 day terms.

Is Isabellenhütte (formerly Isotek) the manufacturer?

Isabellenhütte USA is a subsidiary of Isabellenhütte Heusler GmbH KG, of Dillenburg, Germany. Our high power metal clad resistors are manufactured by RARA.

Where are you located?

We are in Swansea, Massachusetts approximately 60 minutes south of Boston, MA.

How do I interpret your date codes?

You can find date code information in our Support and Resources area.

What happens if my package arrives damaged?

All our packages come with an orange sticker with full instructions. You must save the original packaging (and packaging material) and call us immediately.

Who is Isabellenhütte?

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).

What does ISA-PLAN® mean?

ISA-PLAN is a technology developed by Isabellenhütte Heusler, GmbH KG of Dillenburg, Germany. This technology consists of 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.

What does the “R” indicate in your part numbering system?

The “R” represents the decimal point e.g. R010 is 0.010 ohms.

How are your parts packaged?

Please see the component data sheets for packing information.

Are your components RoHS compliant?

Most are. Please visit our Support and Resources area for documentation.

Do you have Reach information?

Yes, please visit our Support and Resources area for documentation.

Which products carry UL approval?

Most of our high power, metal clad resistors are UL 508 and CSA approved. Please visit our Support and Resources area for UL file information.

Are your parts AEC Q200 qualified for the automotive industry?

Many of our surface mount resistors are AEC Q200 qualified. Parts that are qualified will have a notation on both the product page and the data sheet.

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?

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.

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?

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.

What is ISA-WELD®?

ISA-WELD® is a technology developed by Isabellenhütte Heusler, GmbH KG of Dillenburg, Germany. ISA-WELD® is a process by which copper is electron beam welded to a given alloy under vacuum to form a homogenous material from which resistive shunts can be produced. This process offers a wide range of options in terms of both design and production.

Why are the ISA-WELD®- and some of the ISA-PLAN®-SMD current-measuring resistors of the component families BVE, BVS, BVT, BRS, VMx and VLx only offered as two-terminal?

Through a suitable layout of the sense connections on the circuit board a four-terminal measurement can be realized in the application with a two-terminal resistor. A rise of the TC due to the copper protective resistor is only noticed at values < 5 mOhm.

How does one understand the pulse-load diagram?

The pulse-load diagram specifies the maximum pulse power or energy as a function of the pulse length for a resistance value of the product series, which the component withstands without appreciable resistance drift even after more than 1 million cycles. Since the pulse loadability is dependent on the layout and the foil thickness and therefore on the resistance value, in particularly critical cases this loading limit in the test is to be fixed separately.

How can the estimated loading limit be determined for a short-circuit (max. 1 to 5 times, no continuous cyclic load) on the ISA-PLAN® precision resistors?

Only by means of detailed laboratory tests, which we are happy to carry out for our customers.

What happens with an ISA-PLAN® high precision resistor at extreme overloading?

With extreme overloading the resistance path can melt, the component becomes highly resistive or becomes an open circuit.

Are ISA-PLAN®- or ISA-WELD® high precision resistors combustible?

No, up to now this has not been an issue.

Is a continuous load exceeding the value specified as continuous-/nominal load on the data sheet permitted, if the max. contact point temperature is significantly below the power-derating curve?

Because of the particularly low thermal resistance, e. g. at room temperature, the components can be loaded significantly higher than specified in the data sheet. Laboratory testing is required to determine the exact limits of specified components.

Which resistance values are normally available for ISA-PLAN®- and/or ISA-WELD® high precision resistors?

As standard the values are based on the E-12 series. Beyond this, normally the values with 2 and 5 mΩ are also available (e. g. 2 mΩ, 20 mΩ, 200 mΩ, 5 mΩ, 50 mΩ, 500 mΩ).

You normally use Manganin® as resistance alloy in the resistors. The temperature coefficient of Manganin® is specified with < ± 10 ppm/C. Why do you mostly specify your SMD resistors < ± 50 ppm/C on the data sheets?

For a two-terminal, the TC of a component is comprised of the TC of the resistance material (e. g. Manganin®) and the not completely avoidable influence of the supply line or bonding. For that reason we usually specify the TC of a two-terminal with < 50 ppm/C.

Between which measuring points on the resistor is the R(thi) determined?

Normally in between the contacts/soldering points and the hot spot (in the middle of the resistor). For ISA-Weld products between the copper (1mm from the welded seam) and the middle of the resistor.

What must one pay attention to if 2 or more resistors are connected in parallel?

BVS in Parallel pdf is the literature library.

Which requirements/specifications are necessary and helpful for choosing the ideal measuring shunt?

Besides the preferred assembling technique and the resistance value, the continuous or pulse load of the component and the required tolerance are the decisive factors.

For many SMD resistors, in the technical data stability section you specify < 1 % after 2000 h. In the diagram of the data sheet this value is significantly lower, namely at approx. < 0.25 %, even up to 5000 h, why?

The typical drift of the components is about < 0.25 %. The specified tolerance < 1 % is the absolute upper limit for the drift, respectively the maximum load according to the load reduction curve.

What can happen in the worst case when an ISA-WELD® resistor (electron-beam-welded copper-Manganin®-copper) is overloaded?

The precision resistors of the ISA-WELD® series are very robust and in practice, especially as SMD resistors, almost indestructible. On SMD resistors the soldering point is destroyed, for otherwise bonded ISA-WELD® resistors, the resistance material can melt at temperatures > 1000 °C.

Especially with the high-impedance SMx series, under certain circumstances a concave sagging of the component can occur after soldering. What influence does this change have on the resistor?

The characteristics of the component are not influenced by this. The cause for this is the separating resin web with its high expansion coefficients.

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