BS 791:1990 pdf free.Specification for Solid-stem calorimeter thermometers.
BS 791 The thermometer shall be calibrated for use at totalimmersion, i.e.the reading is taken when the thermometer is vertical and immersed at least tothe end of the liquid column in the medium, thetemperature of which is required to be measured, orfor use at partial immersion.
NOTE The purchaser should specify in the enquiry or orderwhether a partial immersion thermometer is required.
On partial immersion thermometers, a line shall beetched at least halfway round the stem of the
thermometer at the level to which it is intended tobe immersed.
The stem shall be made of lead glass or otherthermometric glass appropriate to the temperaturerange and shall have an enamel back.The bulb shall be cylindrical and in alignmentwith the stem. Its external diameter shall notexceed that of the stem. It shall be made of athermometric glass approved by the NationalPhysical Laboratory (see Appendix A).
The glass shall be so selected and processed thatthe finished thermometer shows the following characteristics.
a) Stress in the glass shall be reduced to a levelsufficient to minimize the possibility of fracturedue to thermal or mechanical shock.
b) ‘The thermometer shall be stabilized beforegraduation using a process such that the scaleerror and interval error of the finished
thermometer are within the limits specified inclause 9.
c) The legibility of the reading shall not beimpaired by devitrification or clouding.
d)The image of the meniscus shall be distorted aslittle as possible by defects or impurities in theglass.
Above the mercury, the thermometer shall be eithervacuous or gas-filled; in the latter case, only a dry,inert gas shall be used.The indication of a gas-filledthermometer, when the meniscus is at the top of thescale, shall not change by more than 0.01 C whenthe temperature of the gas above the mercury ischanged by 3o℃.
The cross-sectional area of the bore shall not showvariations from the average greater than 5 %, andthe shape of the bore shall be such that, withouttapping, jumping of the meniscus does not exceedone half of the graduation interval, when the
temperature is rising at a uniform rate not exceeding 0.05°Clmin.In the case of a thermometercalibrated for use at partial immersion, the volumeof mercury contained in the capillary tube betweenthe immersion line and the lowest figured scale lineshall not exceed the equivalent of 2°C.BS 791 pdf download.