15
Bath Use
General
6 Bath Use
Caution: Read before placing the bath in service
The information in this section is for general information only. It is not de signed to be
the basis for calibration laboratory procedures. Each laboratory will need to write their
own specific procedures.
General 6.1
Be sure to select the correct fluid for the temperature range of the calibration. Bath
fluids should be selected to operate safely with adequate thermal proper ties to meet the
application requirements. Also, be aware that some fluids ex pand and could overflow
the bath if not watched. Refer to Section 8.3, Bath Fluid, and subsequent subsections
for information specific to fluid selection and to the MSDS sheet specific to the fluid
selected. Generally, baths are set to one temperature and used to calibrate probes only
at that single temperature. This means that the type of bath fluid does not have to
change. Additionally, the bath can be left energized reducing the stress on the system.
The bath generates extreme temperatures. Precautions must be taken to prevent
personal injury or damage to objects. Probes may be extremely hot or cold when
removed from the bath. Cautiously handle probes to prevent personal in jury. Carefully
place probes on a heat/cold resistant surface or rack until they are at room temperature.
It is advisable to wipe the probe with a clean soft cloth or paper towel before inserting
it into another bath. This prevents the mixing of fluids from one bath to another. If the
probe has been calibrated in liquid salt, carefully wash the probe in warm water and
dry completely before transferring it to another fluid. Always be sure that the probe
is completely dry before inserting it into a hot fluid. Some of the high temperature
fluids react violently to water or other liquid mediums. Be aware that cleaning the
probe can be dangerous if the probe has not cooled to room temperature. Additionally,
high temperature fluids may ignite the paper towels if the probe has not been cooled.
For optimum accuracy and stability, allow the bath adequate stabilization time after
reaching the set-point temperature.
Comparison Calibration 6.2
Comparison calibration involves testing a probe (unit under test, UUT) against
a reference probe. After inserting the probes to be calibrated into the bath, al low
sufficient time for the probes to settle and the temperature of the bath to stabilize.
One of the significant dividends of using a bath rather than a dry-well to cali brate
multiple probes is that the probes do not need to be identical in construc tion. The fluid
in the bath allows different types of probes to be calibrated at the same time. However,
stem effect from different types of probes is not to tally eliminated. Even though all
baths have horizontal and vertical gradients, these gradients are minimized inside the
bath work area. Nevertheless, probes should be inserted to the same depth in the bath
liquid. Be sure that all probes are inserted deep enough to prevent stem effect. From
research at Hart Scien tific, we suggest a general rule-of-thumb for immersion depth
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