Thermocouple : A thermocouple (or thermopile) consists of two wires of different metals together, producing a voltage that varies with the temperature of the connection. Using different pairs of metals for different ranges of temperature, being very wide margin set: from -248 ° C to 1477 ° C. The thermocouple is the most accurate thermometer in the range of -631 ° C to 1064 ° C and, as is very small, it can respond quickly to temperature changes.
Liquid in glass thermometers : The glass thermometer should be chosen for its stability and should be well annealed. The bulb, high temperatures and pressures, is exposed to permanent increase in volume, causing an indication of the thermometer is lower than it should.
Mercury thermometers are more accurate and calibrated graduates for total immersion, that is, with all the mercury, including the tube, the temperature is: measured. If part of the mercury column extends outside the region that has been measuring the temperature, apply a correction to the reading, based on the length of the column degrees pop in the temperature difference between the column emerging and the bulb and the relative ditalación of mercury and glass.
Beckmann thermometer : Beckmann differential thermometer has a scale of 30 cm long, aproximadariiente with a full-scale 5 6 6 degrees C. divisions. of 0.01 degree. It is constructed so that a portion of the mercury bulb can be moved to a warehouse in a leading end of the column of mercury to the graduate section for temperature zones that are to measure the differences. It is only used to measure temperature differences cle. The accuracy achieved is between 0.002 and 0.005 degrees in the measure of any interval within the limits of the scale.
Pyrometers : The radiation pyrometer is used to measure high temperatures. It is based on heat or visible radiation emitted by warm objects and measure the heat radiation by a thermocouple or visible light radiation, compared with incandescent tungsten filament connected to an electrical circuit. The pyrometer is the only thermometer that can measure temperatures above 1477 ° C.
We hear that matter expands when heated and this expansion is not always linear. We also know that alcohol and mercury were initially the liquids used for the construction of thermometers. Clearly, not all thermometers are built this way, but because they are the most common, we’ll start them: the thermometers of this type consist of a glass tube with an inner diameter very small (capillary) soldier a glass sphere containing the liquid selected. The more liquid, the expansion of warming is more noticeable and therefore the rise in the capillary tube, easier to observe.
Surely you have thought that if the bodies expand by heat, it also thins the glass in which is contained the liquid. Will it change the fact the accuracy of the measurement? Dilatation of the glass scale is so small that we can dismiss it, only for very accurate to be used other methods. It is important to consider that for this reason the readings in glass thermometer with an accuracy of 0.01 K.
All liquids freeze and boil at specific temperatures, therefore, each thermometer is designed for specific temperature ranges. In the case of mercury, its freezing point is -39.0 ° C and the boiling point is 356.7 ° C, values ??that limit their range of application. For the same reason, an alcohol thermometer works only in a range from -100 ° C to 70 ° C. Here are the list of some common thermometers
- Gas thermometer
- Platinum resistance thermometers
- Several thermometric probes for use with a digital thermocouple thermometer laboratory
- The temperature inside a furnace is measured with a thermometer or pyrometer radiation
- EXPANSION THERMOMETERS
- Bimetallic strip thermometer
- Thermometers filled systems
- Gas filled thermometers
- Thermometers vapor pressure
- Thermometer pressure steam pressure-sensitive element
- Liquid expansion thermometers