MIL-T-24388C

Abstract

This specification covers environmentally hardened resistance thermometers and thermocouple sensors that transform the surrounding thermal energy in a manner that can be electrically measured and converted to a temperature using a signal conditioner/temperature monitor. Types of configurations covered in this specification are those which place the resistance thermometer or thermocouple sensor directly into the medium (bare bulb), into a thermowell, or embedded into a bearing. <br>Resistance thermometers and thermocouple sensors shall be classified according to the following variables: </span><pre> <b>Designation</b> <b>Type</b> <b>Configuration</b> <b>number</b> (see <a>1.2.1</a>) (see <a>1.2.2</a>) (see <a>1.2.3</a>)</pre> <br> <br>The type of resistance thermometer or thermocouple sensor shall be designated by one of the following three-letter symbols. <pre> <b>Type</b> <b>Symbols</b> Type K thermocouple sensor KTC Resistance thermometer with nickel element NRT Resistance thermometer with platinum element PRT</pre> <br> <strong>Beneficial comments (recommendations, additions, deletions) and any pertinent data which may be of use in improving this document should be addressed to: Commander, Naval Sea Systems Command, SEA 55Z3, Department of the Navy, Washington, DC 20362-5101, by using the self-addressed Standardization Document Improvement Proposal (DD Form 1426) appearing at the end of this document or by letter.</strong> <br>Type of configuration for which the resistance thermometer or thermocouple sensor is intended shall be designated by one of the following two-letter symbols. <pre> <b>Type of configuration</b> <b>Symbols</b> Thermowell TW Bare bulb BB Embedded EM</pre> <br> <br>The designation number used to specify the sheath length and other applicable parameters within each type of configuration shall be denoted by one or two numerals or by one or two numerals preceded by a letter found in one of the following: <pre> <b>Type of configuration</b> <b>Table number</b> TW II BB III EM IV.</pre> <br> <br><b><u>Intended Use:</u></b> Resistance thermometers and thermocouple sensors are intended to sense a temperature and convert this to an electrical output for input to a temperature signal conditioner. Resistance thermometers have the following characteristics: a. The two resistance thermometer elements have different temperature ranges (excluding the EM configuration): Nickel minus 40 to 400 &#176;F Platinum minus 40 to 1000 &#176;F. b. High accuracy c. Excellent stability and reproducibility but slow in response d. Easily interchangeable but damages easily if not handled properly. Can be matched to close tolerances for temperature difference measurements. e. Resistance thermometers with platinum elements should be specified for new construction and new instrument installations. Resistance thermometers with nickel elements should be restricted to retrofit and replacements only. Thermocouple sensors have the following characteristics: a. Simple construction b. Small signal output is produced which requires sensitive measuring instruments. c. Lower cost and faster response time than the resistance thermometer. d. Type K thermocouple covers a temperature range of minus 40 to 1500 &#176;F (excluding EM configuration). e. Compensation for reference junction temperature is required. f. Attains high accuracy but subject to changes within the accuracy limit with use. These changes become more pronounced as the temperature increases. g. Preferable for use with thermowells having a 2-inch immersion depth since the thermocouple sensor's minimum immersion depth is significantly smaller than that of a resistance thermometer. h. Preferable for use in the EM configuration since extremely fine resistance thermometer element wire is very susceptible to electrical opens, shorts, or intermittent behavior in service. Resistance thermometers with platinum elements should be specified for new construction and new instrument installations with the following exceptions: a. Thermowells have a 2-inch immersion depth (see <a>6.1.1.2(g)</a>). b. EM configuration installations (see <a>6.1.1.2(h)</a>). <br>