Various tests are performed to ensure the quality of the sensor:
- Type Test: Such testing that is usually performed to demonstrate compliance with the specification is called a type test. The purpose of such a test is to show the general characteristics & design of a particular sensor sample.
- Routine Test: Such a test that is performed on each sensor according to the sampling plan is known as the routine test.
Important quality assurance tests are as follows:
- Inspection of Appearance & Construction: Visual inspection ensures conformance of thermocouple assembly to specification, drawing & materials. The finish of seams, joints, welds, name-plates/tagging-plates and other parts are visually inspected for any defects, dirt and roughness on the surface. If needed, welds and fittings can be subjected to a dye-penetration-test, hydrostatic pressure testing and even X-ray inspection.
- Dimensional Checks: Unless otherwise stated, dimensional checks are made according to the tables using a straight gauge, Vernier Caliper, and even gauges.
- Insulation Resistance Test: Such testing is usually performed with a super megohmmeter by applying a steep temperature gradient to the sensor assembly that has been immersed in a boiling water-bath for accelerating the condensation of residual moisture in the assembly. Such testing allows a very precise measurement of the assembly’s insulation resistance between the sheath and the terminal.
- Emf Calibration Tests: Such a test could be performed by two ways, one with the standard method with RTD or standard thermocouple, and second option is by the absolute method using fixed point standards in each unit or set at 3 points of the preset temperature as per the sensor type.
- Pressure Tests (Only for Elements That Are Sealed): The element would be tested in a hydraulic testing chamber where ice & water are in equilibrium, and they are electrically connected to a suitable indicator. The fluid pressure in the chamber should be increased to 35 kgf/cm, and then maintained for 15 mins. The element’s resistance or EMF must not deviate considerably enough from the equilibrium temperature that corresponds to the applied pressure, and when the element is later removed from that chamber, it must pass the accuracy test as well as the insulation resistance testing.
- Thermocouple Type Identification Test & Polarity Test: Either immersing the thermocouple in the boiling water bath above or applying hot air/flame heat to the hot-end/cold-end of the bead thermocouple to produce an EMF that allows a certain type of thermocouple to be plotted on Temperature vs. EMF-table. A DC circuit tester that is high in resolution tends to be utilized for identifying the thermocouple type & the polarity of the thermocouple’s terminal & its leg.
- Others: Loop Resistance tests, pressure tests, X-ray tests, vibration tests, voltage withstand tests, helium leak tests, etc. could even be done if requested.
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