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6
Bath Use
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.
6.1
General
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 General Operation,
Section 8, 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 en-
ergized 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 in-
serting 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 danger-
ous if the probe has not cooled to room temperature. Additionally, high temper-
ature 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.
6.2
Comparison Calibration
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,
6 Bath Use
General
19
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