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Resistance Bridges
Resistance bridges are one of the most expensive pieces of lab
equipment you can buy. Most sell for $30,000 to $50,000. The
resistance bridge market is very small, and there’s hardly any
competition. There’s nothing to control the price except your
willingness to pay.
Resistance bridges are difficult to use. Their learning curve is
long and complex, which means you’ll spend plenty of time learning
to master one. Time spent learning costs you money, and costs
multiply if you have to train other people!
So
why buy a bridge if you have a legitimate alternative?
If
1 ppm accuracy gets the job done, the easiest and cheapest way to
do it is with one of Hart’s Super-Thermometers.
Hart 1575A
The 1575A Super-Thermometer is a best-selling thermometer because
of its ease of use, high accuracy, built-in software, and
reasonable price. Temperature is read directly on the display in
your choice of scales. There are no manual
resistance-to-temperature conversions. Resistance is converted to
temperature for you using the ITS-90 algorithm in any one of the
instrument’s ranges. Up to 16 independent sets of probe
characterizations can be stored in the 1575A’s memory. Switch
SPRTs and simply call up its reference identification number.
Forget the extensive, time-consuming setup required by resistance
bridges. Read the features common to both units and you’ll
understand why each is a great buy.
Hart 1590
The 1590 Super-Thermometer II has all of the features of the
1575A, plus it has the unbeatable accuracy of 1 ppm and a color
screen that tilts to create the best viewing angles. With all of
these features, it’s still less than half the price of a bridge.
In
many labs with standards that require the use of bridges,
Super-Thermometers have been accepted as an alternative to bridges
because they are a combination of bridge technology and
microprocessor-based solid-state electronics—and they’re much
easier to use.
Both Hart Super-Thermometers come with an accredited calibration.
Accuracy
In addition, resolution with a 25-ohm SPRT is 0.0001°C. Comparison
calibrations or calibrations against primary standard fixed points
are easily performed. Both instruments have two channels for
handling two probes at once. Display and record actual
temperatures or choose to read the difference between the two
directly from the screen.
Both Super-Thermometers have their own on-board resistors. Each is
a high-stability, low thermal coefficient, four-terminal resistor
for each of the resistance ranges of the thermometer: 0.25 ohms,
2.5 ohms, 10 ohms, 25 ohms, 100 ohms, and thermistor ranges.
Resistors are housed in an internal temperature-controlled oven.
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