Hart scientists have designed and tested ITS-90 fixed-point cells for many years. Not only do we manufacture all the major fixed points, our metrologists have written extensively on the theory and use of cells and have created new designs covering a range of applications no other company can match.

Our testing of fixed-point cells is also unmatched. The scope of our accreditation includes the testing of ITS-90 fixed-point cells. Each cell may be purchased with this intercomparison option, which includes comparing the equilibrium value of your cell against that of a reference Hart cell.

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Hart Scientific’s temperature calibration baths are known around the world as the best calibration baths made. If you’re looking for a cold bath, no one gives you more choices than Hart.

These five baths operate at temperatures as low as –40 °C, and each one is built using CFC-free refrigerants. Hart’s proprietary controller design and unique tank construction produce bath stabilities to ±0.001 °C or better. These baths are so stable and uniform that national labs use them for comparison calibrations and fixed-point cell maintenance.

Each bath (except the 7011) is fully automatable with a bath interface package and Hart’s MET/TEMP II automation software package. When we automate a bath, we automate it completely with computer-controlled solenoid valves for precision balancing of the heating and cooling system. MET/TEMP II performs all calibration tasks automatically, using your PC.

With a Hart cold bath, you can forget external coolants. Internal refrigeration systems are all that’s needed to reach each bath’s coldest temperature. Most cold baths may be ordered with an optional pumping lid for supplying external cooling requirements.

Each bath has unique characteristics that make it perfect for specific jobs. Some baths are excellent for SPRTs, some are great with thermistors, and some are perfect for maintaining triple point of water cells. A 7008IR bath can even be used to maintain the temperature of a blackbody cone.

Regardless of your application, Hart has a bath that gets the job done, and done better than anyone else can do it. Call us today and tell us about your application.

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If the reason you don’t use fixed-point cells is because they’re too expensive or too difficult to use, you haven’t heard of Hart’s mini fixed-point apparatus.

The triple point of water (0.01 °C) is one of the most important temperatures on the ITS-90. Unfortunately, realizing and maintaining triple point of water cells hasn’t always been convenient or cost-effective.

Because ITS-90 calibrations require frequent measurements at the triple point of water, and because the triple point of water is often used as a statistical check against the drift of a temperature standard, it is important to be able to realize and maintain well-constructed triple point of water cells easily.

Hart’s 9210 TPW Maintenance Apparatus provides built-in programming for the simple supercool-and-shake realization and maintenance of our 5901B Mini TPW Cell. Simply insert the cell, enter the “freeze” mode through the front-panel buttons, have your morning cup of coffee, and when the 9210 audibly alerts you, remove the Mini TPW Cell and give it a shake to initiate freezing a portion of the water. Re-insert the cell, change the program mode to “maintain,” and you’ve got 0.01 °C for the rest of the day with uncertainty of only ±0.0005 °C.

Precision-machined thermal blocks can also be used to take advantage of the excellent stability and uniformity of the 9210 for performing comparison calibrations. Multi-hole and custom blocks are available with 178 mm (7 in) depths.

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The 92XX makes using fixed points easy. Simply insert the cell at the end of the day and let it sit overnight. The next morning, initialize the built-in software routine for your specific cell. Come back in an hour, verify the stability of the cell, and you can take measurements for the rest of the day from a near-perfect temperature source!

The built-in software lets you choose between using melting-point curves or freezing-point curves for each metal. The ITS-90 calls for freezing points, but melting points are easier to realize, and the difference in uncertainty (less than 2 mK for most applications) is generally insignificant. In fact, the difference between using traditional cells at their freezing points and Hart’s mini cells at their melting points is not significant for most labs in most applications.

Gallium Point Cell 15 °C to 35 °C
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All other Cells 50 °C to 680 °C
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Several companies manufacture high-quality resistance bridges for both AC and DC applications. All of these bridges can take measurements at the 0.1 ppm level, and research has shown that all of them compensate well for any theoretical inaccuracies predicted in their design.

We like the MI bridge because we feel confident about its measurements, and its software gives us more information than we can get from the other instruments. While it’s true we do use the other bridges for certain functions we undertake in our lab, including some experimental testing, we use the MI bridge every day for fixed-point calibrations of SPRTs.

The 5581 Bridge performs a true auto-balancing procedure to nine significant digits. As the check proceeds, the bridge steps through an internal comparison of the transformer’s windings, the results of which are recorded to track its performance over time.

Another function of this bridge is its real-time uncertainty analysis program. In this mode you enter external uncertainty factors such as the uncertainty of your resistor, and the 5581 combines your information with its own uncertainties to compute a system uncertainty for your measurement.

The optional Windows-control software offers history logging and regression analysis along with uncertainty analysis and the auto-self-check feature. The program also calculates standard deviations if you need them. You can enter coefficients for your SPRT and read temperature rather than resistance.

Of course, if you prefer, you can operate the bridge manually. The choice is yours, but either way you’ll find this to be a great bridge to use.

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