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User's Guide
6-2
The immersion depth for standards is dependent on several factors including
accuracy requirements and type of liquid. Therefore, we recommend a 152 mm
(6 inches) minimum immersion depth. However, remember the handle limitations.
The handle is not designed to be immersed. The temperature limits of the handle
are 0 °C to 80 °C. Temperatures outside these limits can damage the handle.
Convection of heat from the heat source must be kept within the handle limits.
The exact immersion depth required can be determined by performing a gradient
test taking measurements approximately every 1.27 cm (.5 inches) until there is a
significant difference in readings. Allow the thermometer to stabilize at each new
depth. Plot the results to see the stem effect.
6.4 Thermal EMF
Two factors contribute to thermal EMF, chemical consistency and physical
consistency. Variations in chemical structure due to impurities can contribute to
thermal EMF. Also discrepancies in crystal structure can contribute to thermal
EMF. These factors are minimized by annealing the full length of wire before
construction of the PRT.
Likewise, connection to extension lead wires and readout instruments can be a
source of thermal EMF. The thermal EMF is caused by a difference in
temperature between two connections. If the two connections are the same
temperature, there will be little or no thermal EMF effects. However, if there is a
substantial temperature difference between connections, the thermal EMF effects
will be significant. Therefore, cover or insulate any exposed bridge or
galvanometer terminals to lessen the source of error. The effects of thermal EMF
can be canceled by using an AC bridge or a DC bridge with reversible current.
1.888.610.7664 sales@GlobalTestSupply.com
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