BS 1904:1984 pdf free download.British Standard Specification for Industrial platinum resistance thermometer sensors.
1. Scope
BS 1904 specifics requirements for industrial platinum resistance thermometer sensors whose electrical resistance is a defined function of temperature. The standard covers thermometers suitable for all or part of the temperature range —200 °C to +850 °C with two tolerance classes. It is primarily concerned with sheathed elements suitable for immersion in the medium whose temperature is to be measured.
Methods of test to prove compliance with this standard and suitable apparatus for some of the tests are also described.
2. Defirihions
2.1 Platinum resistance thermometer sensor
A temperature-responsive device consisting of a sensing resistor within a protective sheath, internal connecting wires and external terminals to permit connection of electrical measurement devices. Mounting means or connection heads may be included. Typical constructions are shown in Figure I.
Noses 1. — This resistance thermometer sensor is referred to as a thermometer in subsequent clauses of BS 1904,
2. This definition excludes any separable pocket or well provided with the thermometer.
3.4 Electrical supply
Thermometers shall be constructed so that they are suitable for use in measuring systems using direct current or alternating current at frequencies up to 500 Hz.
3.5 Connecting wire configuration
Thermometers may be constructed with a variety of internal connecting wire configurations. Identification and designation of the terminals is therefore essential. Figure 3 shows the preferred methods.
3.6 Thermometer identification
Each thermometer shall be marked to indicate resistance class, connecting wire configuration, and temperature range, for example:
When the sensing resistor is mounted in its sheath the insulation resistance between each terminal and the shcath shall be measured with a test voltage between tO V and 100 V d.c. and under ambient conditions between 15 °C and 35 °C and at a relative humidity not exceeding 80%. The polarity of the test current shall be reversed. In alt cases the insulation resistance shall be not less than 100 M when the value has stabilized.
4.2.2 Resistance tolerance
The resistance calibration of the thermometer shall be within the tolerance values specified in Sub-clause 3.3 when tested with a current such that the electrical power dissipated in the thermometer does not cause a rise of temperature due to self-heating in excess of Vs the tolerance value at the temperature.
The test for Class A thermometers shall be carried out at two or more temperatures suitably spaced over the stated working range and with the thermometer inserted in the test medium to at least the declared calibration immersion depth (see Sub-clause 5.2).
The test for Class B thermometers shall be carried out at one temperature, normally the ice point.
4.3 Type tests
4.3.1 Insulation resistance
A knowledge of the insulation resistance is important in the design of associated circuitry.
The test shall be that specified in Sub-clause 4.2.1. An additional test shall be carried out at a test voltage not exceeding 10 V d.c. with the thermometer at the rated maximum
For response times less than I s, the test apparatus should be designed so that the water has no free surface in front of or behind the thermometer so as to avoid problems of air entrainment. The velocity v within the usable cross-section shall be 0.4 ± 0.05 rn/s. The initial temperature shall be within the limits of S °C and 30 °C. The temperature step shall be not more than 10 °C.
The final temperature of the water shall not vary by more than ± I % of the temperature step during the duration of the measurement.
The minimum immersion depth shall be equal to the sensitive length of the thermometer plus five times its diameter.
Where the designed immersion depth of a thermometer is less than the above-mentioned value, the test should be performed at the designed immersion depth. This immersion depth shall be mentioned in the test report.
4.3.4 Sdf-heaiing
This test shall bc carried out with the thermometer immersed to the declared calibration immersion depth in well-stirred water maintained at the ice point. Suitable apparatus for testing the thermometer immersed to the calibration immersion depth is described in Appendix B.
The steady-state resistance shall be measured with a current such that the power dissipation in the thermometer is not more than 0.1 mW.
In the case of the nominal 100 fl resistance thermometer the steady-state resistance shall then be measured at the manufacturer’s stated maximum rate current, or 10 mA, whichever is less. The equivalent figure for the nominal 10 1) thermometer is 30 mA. The temperature rise equivalent to the measured increase in resistance shall not exceed 0.3 °C.
This test should be conducted if possible with the thermometer mounted in the same manner as that in which it is to be used.
The mounting means shall be rigidly attached to the vibrator and the thermometer shall be vibrated over the frequency range of 10 Hz to 500 Hz with a forcing acceleration of 20 rn/s2 to 30 m/s peak-to-peak. The frequency range shall be swept at a rate of one octave per minute for a total period of 150 h. The vibrations shall be applied to the thermometer in axial and transverse directions each for one half of the total period. The frequency and nature of any resonances shall be noted. The electrical continuity shall be monitored continuously. At the conclusion of this test the thermometer shall be tested to ensure continued compliance with the insulation resistance requirements of Sub-clause 4.2.1. The thermometer shall also be tested to verify that the resistance at the ice point shall not have changed by more than the equivalent of 0.05 °C.
4.4.3 Pressure lest
This test is intended to apply to a thermometer supplied by a manufacturer as suitable for pressure tight insertion in a vessel without further protection.
It is to establish suitable electrical behaviour and is not to supplant tests for mechanical suitability for use under pressure.
The thermometer may be tested in a pressure tube filled with water. The tube, having only a small clearance around the stem of the thermometer, shall be made of stainless steel and should be as thin as is consistent with the pressure requirements. The tube such as shown in Figure B2. page 37, of Appendix B may be inserted in the apparatus described in Appendix B so that the thermometer is below the surface of the ice water to at least the calibration immersion depth.