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Selecting a Thermometer |
Selecting a Thermometer
When selecting a thermometer, it is important to consider the dial or case size,
stem or capillary length, the connection type and the temperature range. To
ensure safety and accuracy, thermometers should be selected while giving
consideration to the measured media and the ambient operating conditions.
Improper application may be detrimental to the thermometer, causing failure and
possible personal injury or property damage. Ningfeng has four (4) basic types
of thermometers to select from; Bi-metallic, Remote Reading, Industrial and
Laboratory. All four basic types may appear suitable for any typical
application, however, the correct selection depends upon the industry being
served and the application specified.
Bi-metal Thermometers
Ningfeng Bi-Metal Thermometers are direct sensing instruments, that are
hermetically sealed and thus completely waterproof. For accurate temperature
readings, the stem should be immersed at least 63mm (2.5¡±). All Bi-metallic
thermometers are of stainless steel construction to protect against corrosive
conditions. An external adjustment screw is conveniently located on the back of
each case for easy field recalibration of thermometers.
Remote Reading-filled Thermometers Remote Reading Thermometers are instruments
used to measure temperature from a remote source. By means of a capillary tube
with a sensing probe at one end and an indicating dial at the other end,
temperatures can be determined from a source that is up to a 100 feet (30 metres)
away.
Ningfeng Remote Reading Thermometers are either gas or vapour filled.
Gas filled dial thermometers are designed for industrial applications requiring
accurate and uniform response over the entire range. The entire system is filled
under pressure with inert gas for positive movement, accuracy and sensitivity.
The accuracy delivered by this system is 1¼2% of full scale value when the
temperature measured is in the mid-scale of the dial.
Vapour tension thermometers provide economical and reliable remote reading
service for most industrial applications. Vapour tension thermometers have
non-linear scales (non-equal graduations across the entire scale). To ensure
exceptionally close readings, the operating temperature should fall in the upper
half of the thermometer¡¯s scale. The accuracy delivered by this system is ¡À 3%
of the the full scale.
Both Celsius and Fahrenheit scales are available in gas and vapour formats in
either single or dual scales. Please note that the selected temperature range
should be approximately twice the normal operating range anticipated and the
maximum temperature should not exceed 75% of the full scale.
Cases are available in numerous sizes and made of steel, stainless steel,
phenolic and cast aluminum; capillaries are available as copper braided and
stainless steel (with or without flexible armour), in an assortment of lengths;
and the bulb is available as a standard 150mm (6¡±) x 13mm (1¼2¡±) in brass and
stainless steel, Ningfeng recommends using a stainless steel bulb & capillary
for all process temperatures above 5000F.
Finally, consideration must also be given for the medium to be measured, ambient
temperature, humidity, installation in-doors or out, presence of dust, corrosive
atmosphere, mechanical shock and, frequency and magnitude of vibration.
Industrial Glass Thermometers
Ningfeng industrial thermometers are available in both 9" (230mm) and 5" (130mm)
scales. These thermometers have a glass tube filled with liquid which expands or
contracts according to reflections in the temperatures. Installation variations
include fixed bottom, fixed back and fully adjustable. Brass separable
thermowells come standard on both types of industrial thermometers.
Laboratory
Laboratory thermometers fulfill a specific need in various applications
including quality control. Scales are available from 5" (130mm) to 20" (500mm).
Standard ranges are available in Celsius or Fahrenheit. These thermometers have
a glass tube filled with liquid which expands or contracts according to
reflections in the temperatures. Fillings include mercury, red-reading mercury
or red alcohol. Protective armours are also available in various materials,
including stainless steel.
Thermowells
Thermowells must be used on any application where the stem of the thermometer
may be exposed to pressure, corrosive fluids or high velocity. Additionally, the
use of a thermowell permits instrument interchange for calibration of the
thermometer without disturbing or closing down the process. Ningfeng thermowells
are available in brass and stainless steel with standard thread connections.
Other materials and flange options are available upon request. Thermowell
material should be selected according to the corrosion conditions that the
thermowell will be exposed to.
* Continuous product improvements may result in specifications being changed
without notice. |
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Copyright © 2003-2005,
Cixi Ningfeng Pressure Gauge Factory,
TBP
All rights reserved.
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