Instrumentation Specialist

Thermocouples & RTD’s.

A) AWG was used prior SI standards to specify the diameter of the core of the electrical wires.

B) Both awg and mm2 are used to specify size of cross section of a wire/conductor. The relatioship is found in a standard table – westermann’s tables.

The most common range for differential range for liquid measurement is 0-100. This range is high enough to minimize the errors caused by unequal heads in the seal chambers. It is also dependent on the differences in the temperature of the load lines. The 100 range permits an increased in capacity up to 400. While decrease down up to 20 by merely changing the range tubes or range adjustments.

An orifice tab is welded on the orifice plate which extends out of the line giving an indication of the orifice plate.

A spectacle blind is a blind plate and a plate with line size bore connected together and installed between pipe flanges. This blind may be reversed to blind/deblind a line. It also provides a visual clue as to whether a line is blinded at that location or not.

The bench range/set of an actuator/control valve combination refers to the air pressure required to fully open/close the valve out of line when it is not subjected to process fluid forces.

You may use Ziegler-Nichol’s method ( open loop / closed loop ) or special tuning software tools.

Instrument JB’s depend upon hazards area classification.

JB’s also can be IS or NIS

For IS signal IS JB’s used for NIS signal NIS JB’s used

For analog I/p & o/p signal we can use same JB.

But for Digital I/p & o/p we have to use separate JB’s. Because digital outputs are powered signal, by wrong connection there may be chances to damage the card.

For DCS I/p & o/p and PLC I/p & o/p we used separate JB’s.

Three wire is a better alternative. Primary objective of 3-wire and 4-wire ararrangements to eliminate effects of lead resistance on temp. measurement.

Control valve sizing refers to calculation of flow capacity of a valve for a given fluid, operating conditions and piping arrangement.

Distributed control system(DCS) and Programmable logic controller. These are the control systems which handles fields I/Os.

Primarily depends upon the availability of reliable power supply source.

Density is measured here by measuring the resonant frequency of a vibrating U-tube.

In some equipments a speed below a threshold value but close to zero is referred to as zero speed.

A pcv is a self-actuated pressure control valve used to maintain upstream or downstream pressure at a set pressure using force from the process fluid if necessary.

ASTM stands for American Society for Testing of Materials.

A microswitch is a small switch consisting of a tiny springloaded plunger which operates an electrical contact when actuated. This arrangement is encaged in a plastic housing. It is very commonly found in pressure switches.

It is a transmitter part for allowing process connection to pipe/tube.

A cold junction compensated instrument will typically indicate temperature of the location where the T/C wires are shorted.

A pressure safety valve is used to relieve overpressure by releasing relatively small volumes of material and installed on smaller vessels. A pressure relef valve is used to relieve overpressure by releasing relatively large volumes of material and installed on large vessels/tanks.