What is the maximum length of a capillary for gas actuated thermometers?
Theoretically, the capillary of a gas-actuated thermometer can be up to 100 m long. However, a large probe volume is needed so that the gas-actuated thermometer will operate within class 1. With the expansion thermometer, the maximum length is limited to 15 metres, otherwise the required filling volume would be too great.
How does a gas actuated thermometer operate?
The measuring system of the dial thermometer consists of a stem, capillary and Bourdon tube in the casing. These parts are combined to form a single unit. The entire measuring system is filled with an inert gas under pressure. A change in temperature will cause a change in internal pressure in the stem. The pressure deforms the measuring spring and the deflection is transferred to the pointer via a dial movement. Fluctuations in ambient temperature affecting the casing can be neglected, as a bimetal compensation element is fitted between the dial movement and the measuring spring. The scale ranges are between -200 and +700 °C with an accuracy class 1 in accordance with EN 13190.
Why is liquid damping an advantage with high vibration?
Since the pointer is damped and the temperature can be read better.
Which gas is used as the fill fluid for gas actuated thermometers?
Nitrogen
What influence does the ambient temperature have on the measuring result?
This depends on the following parameters: 1. Ratio of the volume of the probe (tube) to the measuring line and Bourdon tube (rule-of-thumb: 99:1) 2. Length of the measuring line (capillary) - the longer it is, the more the influence 3. Magnitude of the ambient temperature (value), high temperatures cause an offset in the display, low temperatures cause a reduction Possibilities for compensation: 1. via a bimetal compensation spring (opposed to the pointer direction) 2. via error adjustment (only possible if the ambient temperature is known and constant)
What does one mean by the active length of a thermometer?
The active length of a thermometer is the length over which the thermometer effectively averages the temperature, through in-and outflows of the heat.
How long does it take for an expansion thermometer to display the true temperature of the medium?
Rule of thumb: after 90 sec adjustment time, approx. 99% of the measured value has been achieved.
How does an expansion thermometer work?
The measured value registration is made through the liquid-filled measuring system which consists of a temperature probe, capillary and Bourdon tube. All three components combine to form a closed tube system. The internal pressure in the system changes with the adjacent temperature. This causes the pointer axis connected to the spring to turn and the temperature value to be displayed on the scale. The capillary, with lengths between 500 and 10,000 mm also enables measurements to be made on remote measuring points. The scale ranges are between -40 and +400 degC with accuracy classes 1 and 2 in accordance with EN 13190.
How does a bimetal thermometer work?
A strip made from permanently-laminated rolled sheets, made from metals having different coefficients of expansion ("bimetal"), will bend as a result of any temperature changes. The bending is roughly proportional to the change in temperature. For bimetallic strips, two different measurement systems have been developed: helically wound or spirally wound. Through the mechanical deformation of the bimetal spring in either of these spring forms, on any change in temperature a rotational movement occurs. If one end of the bimetal measuring system is fixed securely, the other will rotate a pointer shaft. The scale ranges are between -70 and +600 째C with an accuracy class of 1 and 2 in accordance with EN 13190.
