A pyrometer or thermal imager with a detector
that is sensitive at 1 μm can be used to look through thin glass and measure wall temperatures as the glass emissivity is small and transmission is large. If there is sufficient glass thickness such as in the melt tank, then the bulk glass temperature can be measured.
How does a glass thermometer work?
Liquid-in-glass thermometers are based on
the principle of thermal expansion of substances
. A liquid in a glass tube (called a capillary) expands when heated and contracts when cooled. A calibrated scale can then be used to read off the respective temperature that led to the corresponding thermal expansion.
How does a glass stem thermometer measure temperature?
It consists of a sealed glass tube with a small internal diameter (like a lumen) connected to a reservoir.
Increasing the temperature expands and pushes up the fluid in the reservoir and tube
. A scale on the tube and the location of the expanded fluid indicate the temperature, see Fig. 8.3A.
How does a glass mercury thermometer work?
In a mercury thermometer, a glass tube is filled with mercury and a standard temperature scale is marked on the tube. With changes in temperature, the mercury expands and contracts, and the temperature can be read from the scale. Mercury thermometers
can be used to determine body, liquid, and vapor temperature
.
What is a glass stem thermometer?
A glass thermometer consists of
a stem and bulb
. The stem (long part) of the thermometer has a hollow shaft running almost the entire length of the stem. The bulb of the thermometer contains a small amount of mercury, a metal that is liquid at ordinary temperatures.
Why are glass thermometers not recommended?
Liquid in glass thermometers
tend to be fragile
and hence easily broken, can only be used where the liquid column is visible, cannot be used for surface temperature measurements, cannot be read from a distance and are unsuitable for high temperature measurements.
How accurate is a glass thermometer?
The accuracy of a typical glass thermometer is
±1 scale division
. These are available in partial immersion or total immersion types and typically have to be considerably longer to achieve the same specifications as a mercury thermometer.
How do you calibrate a temperature sensor?
- Calibrating just the electronics with a simulator.
- Calibrating both the electronics and the sensor in a dry-well.
- Calibrating both the electronics and the sensor in a dry-well with a reference thermometer.
What is a digital pyrometer?
A pyrometer is
a type of remote-sensing thermometer used to measure the temperature of distant objects
. … In the modern usage, it is a device that from a distance determines the temperature of a surface from the amount of the thermal radiation it emits, a process known as pyrometry and sometimes radiometry.
How do you test for emissivity?
The emissivity can be determined by one of the following methods, in order of preference:
Determine the actual temperature of the material using
a sensor such as an RTD, thermocouple or another suitable method. Next, measure the object temperature and adjust the emissivity setting until the correct value is reached.
Which is better mercury or digital thermometer?
1.
Digital thermometers provide faster
results. Digital thermometers provide fast results as opposed to mercury thermometers whose readings are slower to realize because you have to wait for the mercury to heat and then slowly rise to display the temperature.
When can glass thermometer be used?
This thermometer is a thin glass tube with a red or blue line inside it. These thermometers are safe to use
for people over the age of 5
. A child younger than 5 may bite the thermometer, breaking it in their mouth. Glass thermometers with galinstan (GAL-in-stan) may also be used to check an oral temperature.
What happens if mercury thermometer breaks?
If you break a mercury thermometer or light bulb,
a small amount of liquid mercury may spill out
. Liquid mercury can separate into small beads, which can roll some distance away. The mercury may also evaporate into vapour. However, this small amount of mercury is extremely unlikely to cause problems for your health.
What is the liquid inside a glass thermometer?
Mercury
, the liquid in the thermometer, is enclosed in a sealed glass bulb that expands into a fine bore present in the stem of the thermometer.
What are the two kinds of liquid found inside a thermometer?
You can identify the liquid in a thermometer based on its color. Silver liquid indicates that the thermometer contains
mercury
, while red liquid is alcohol to which red coloring has been added. Although uncommon in modern thermometers, a clear color indicates water.
What is an advantage of the glass stem thermometer?
One advantage of the glass-stem thermometer is that it:
Does not rely on any mechanical or electronic device that can malfunction
.
