Fluke 7381 - Electrical Resistivity; Fluid Lifetime; Safety; Cost

Calibration Bath
General Operation
17
D
S
= 9.2 / [0.00077 (300-25) + 1] = 7.59 inches (18.98 cm)
Electrical Resistivity
Electrical resistivity is how well the fluid insulates against electric current flow. In some
applications, such as when you measure the resistance of bare temperature sensors, it can be
important that little or no electrical leakage occur through the fluid. In such conditions, choose a
fluid with high-electrical resistivity.
Fluid Lifetime
Many fluids degrade over time because of vaporization, water absorption, gelling, or chemical
breakdown. Often, the degradation becomes significant near the upper-temperature limit of the
fluid, which substantially reduces fluid lifetime.
Safety
With bath fluids, always consider the safety issues. Where there are extreme temperatures, there
can be danger to personnel and equipment. Fluids can be hazardous for other reasons. Some
fluids are toxic. Contact with eyes, skin, or inhalation of vapors, can cause injury. If hazardous or
bothersome vapors are produced, you must use a proper fume hood or adequate ventilation
system.
WWarning
To prevent personal injury, know that fluids at high temperatures pose danger
from burns, fire, or toxic fumes. Use appropriate caution and safety equipment.
Some fluids are flammable and require special fire-safety equipment and procedures. Consider
the fluid flash point. The flash point is the temperature where there is sufficient vapor given off
that when adequate oxygen is present, and an ignition source is applied, the vapor ignites. This
does not necessarily mean that fire is sustained at the flash point.
The flash point can be either of the open cup or closed cup type. Either condition can occur in a
bath environment. The open cup flash point is measured under the condition of vapors that
escape the tank. The closed cup flash point is measured with the vapors contained within the
tank. Since oxygen and an ignition source are less available inside the tank, the closed cup flash
point is lower than the open cup flash point.
Environmentally hazardous fluids require special disposal applicable to federal or local laws after
use.
Cost
Cost of bath fluids can vary greatly, from low cost for water to expensive for synthetic oils. Cost is
important when you choose a fluid.
Commonly Used Fluids
Commonly used fluids and their characteristics are discussed in the subsequent sections.