TILI Automation

 Here we discuss the brief overview of different In-House testing methods carried out for RTD assemblies in the Calibration Laboratory. RTD Testing Methods The below list shows the different testing methods. 1. Calibration RTD calibration can be done as per IEC 751 / DIN 43760 Class A & B. Normally test is conducted for two points (i.e. 00 C & 1000 C), 3 point calibration or more can be followed. 2. Insulation Resistance Test at ambient (room temp.) at 500 VDC It should be more than 100 M ohms. 3. Insulation Resistance Test at 3200 C at 100 V DC IR should be more than 2 M ohms. More than 20 M ohms also can be offered. 4. N2 leakage test For the RTD sensor, after cap welding, the N2 leakage test should be carried out no leakage should be observed at 40 kg/cm2. 5. Response time test Response time test as per IEC 751 – (63.2% step change from ambient to 800C). For RTD without transmitter – 6 to 9 sec up to 6 mm OD of sheath. For RTD with thermowell – the response time will be ...

 Suppose a chemical reactor is heated by steam. A temperature controller varies the amount of steam admitted to a “jacket” surrounding the reactor: Temperature Controller Problem Ever since this process was placed into service, operators have complained about poor temperature control. Several technicians have tried to tune the PID controller, but no combination of tuning constants seems to solve the problem of random reactor temperature fluctuations. Then one day you notice that the “random” fluctuations of temperature are not really random at all: they directly follow fluctuations in steam supply pressure over time. Explain the nature of the control problem (why do variations in steam supply pressure affect the reactor temperature?), and propose a solution for it. Answer: As the steam supply pressure rises and falls, a greater or lesser steam flow will result through the temperature valve (TV) for any given stem position. The simplest and most direct solution to this problem is to...

 RTD measures the temperature in function of variations of its resistance. In order to make them work (4 wire RTD), we need a low current that is called the excitation current. In fact, T ∝ R  and V = IR So T ∝ V If I and R both are variable, measuring the temperature based on voltage V will be wrong! So, to solve this problem we can use the Wheatstone bridge with the known resistors. That is what has been explained in BS 1041-3: “Measurements are made by passing current through a sensing resistor and measuring the potential across it. If the current is known, the potential is a measurement of the resistance and hence the temperature. If the current is not known exactly the potential may be compared with the potential across a known resistor; this is the basis of the bridge systems.” Different arrangements of the Wheatstone bridge allow to measure the temperature in different situations with the accuracy that we need. This is something this is known as 2, 3 and 4 wires RTD sen...

 Temperature Gauges Specification Here we shall see detailed specifications of Temperature Gauges. In general applications, the Bimetallic type of gauges are preferred over filled type gauges. These gauges shall have the following features Manufactured according to SAMA class. Case compensation must be provided Temperature bulb material should be SS 316 as minimum The dial of the gauge shall have following features 150 mm nominal size Black numerals with white background Negative values of temperature should be marked with red color and white background Adjustable head to be provided Provision shall be made for adjustment of pointer without removing from the shaft Gauges shall have weatherproof construction as per IP66. In vibrating conditions, filled type with the capillary extension should be used. The capillary tube shall be made with SS 316 as a minimum. Also, it should have flexible armouring and PVC cover over armouring. Temperature gauges shall have an accuracy of ± 1% FSD (...

 Thermocouple wiring The thermocouple extension wire should meet the requirements of ISA/ANSI MC96.1 or IEC-60584. Thermocouple signals are low-level signals that should be properly shielded and grounded to prevent noise interference with the signal. Insulated hot junctions shall have an insulation resistance to ground of 50 megohms minimum at ambient temperature and 2 megohms minimum at 4508C (8508F). Terminals within the head shall be clearly marked ‘+’, ‘-’, ‘ground’, as appropriate. The multi circuits within heads shall be clearly identified Check that the polarity and continuity of the lead wires are consistent through all the junction boxes from the thermocouple head to the control center Grounded Thermocouple For grounded thermocouples, check that the shield wire is terminated at the grounded thermocouple head in accordance with the manufacturer’s instructions and not at the shield connection on the control center or instrument terminals Un-Grounded Thermocouple For unground...