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PROCESS INSTRUMENTATION

& CONTROL

Selection Of Instrumentation in Mini Plant based on the process conditions, physical location, device

performance and other related factors. Calibration Procedures and Precautions

Considerations taken in installation of instruments

Objectives :

Prepared and presented by: MUHAMMAD FARID BIN MD DAUD (INSEP 01/2013)

SELECTION, CALIBRATION & INSTALLATIONInstrument 1:

TE911(STATION 2)

SpecificationsResistance Temperature Detector (RTD),Type PT100, 3 wire system, length 130mm, range from 0 – 120 deg C.

Process Conditions

Gas Flow Process of high temperature (30-120C) with low velocity (< 300 ft / sec). Process does not involve vibrations and no extreme operations/hazardous area. Process is a little bit noisy due to gas flow.

Physical location

Located on top elbow where mass velocity is high as possible and to be ensured that heat is transferred by convection.

Device performance

High accuracy (±0.1°C) and not easily influenced by external conditions. Temperature resistance is almost linear.High resistivity, melting temperature and large temperature coefficient.


TE911(STATION 2)

SpecificationsResistance Temperature Detector (RTD),Type PT100, 3 wire system, length 130mm, range from 0 – 120 deg C.

Calibration procedures & precautions

Place the reference probe and the unit under test (UUT) in the temperature source in close proximity to one another.Connect the leads to the readout(s) ensuring proper 3-wire connection.Measure the reference probe and determine the temperature. Measure & record the resistance of UUT using 5 point test for as-found / as-left data.Fit in the data and sketch the graph. Identify error type to determine RTD functionality.

Installation Considerations

Installed vertically due to small pipe diameter and to prevent bending.Electrical wires should be run separately with RTD signal wires to prevent inducing extraneous voltages.


TG900(STATION 2)

SpecificationsHelical Bimetallic Temperature Gauge, brand Rueger, meas. range 50 deg F – 400 deg F

Process Conditions

Gas Flow Process of high temperature (30-120C) with low velocity (< 300 ft / sec). Process does not involve vibrations and no extreme operations/hazardous area.Process is a little bit noisy due to gas flow.

Physical location

Surface mounted to the storage tank where the gauge stem is in contact with the process.Gauge is easily viewed locally, flexibly turned to indicate tank temperature.

Device performance

Low cost, less subject to breakage.Covering broad temperature span (350 F).Expansion coeff. are constant over very limited temp. span, high and low uneven.Sufficient accuracy for indication purpose.Sensitive to rough handling.


TG900(STATION 2)

SpecificationsBimetallic Temperature Gauge, brand Rueger, meas. range 50 deg F – 400 deg F


Boiling Point MethodLocate the calibration control for the gauge (usually either a thumbscrew or nut somewhere along the side or back of the gauge).

Prepare a condition where a reference temperature can be made to calibrate the gauge. A boiling water bath is the easiest and safest possible way to do this.

Place the gauge stem in the boiling water bath and wait for the needle to settle on a temperature.


TG900(STATION 2)

SpecificationsBimetallic Temperature Gauge, brand Rueger, meas. range 50 deg F – 400 deg F


If this temperature is 100 deg C / 212 deg F, the gauge is correct. If it is deviated, use the calibration control to correct it. Turn the adjustment in the appropriate direction until it gives a reading of the boiling temperature of water.

Note: Freezing point method is not used due to lowest measuring range > 32 deg F.


FCV91(STATION 2)

SpecificationsFlow Control Valve, Air-to-Close (ATC), bench range 3-10 psi, Cv=4.0, brand Fisher.

Process Conditions

Gas Flow Process of high temperature (30-120C) with low velocity (< 300 ft / sec). Process does not involve vibrations and no extreme operations/hazardous area.Process is a little bit noisy due to gas flow.

Physical location

Sufficient space for installation and routine maintenance of the control valve and its accessories (tubing, positioners, etc.) Travelling position can be easily viewed and measured. Must be equipped with sufficient block & bypass valve in order to ensure proper isolation.

Device performance

Good rangeability and turndown ratio.Low hysteresis / dead band errors.Good response time and fail safe operation. Optimum trim design and sizing to ensure correct valve capacity accordance to process conditions.


FCV91(STATION 2)

SpecificationsFlow Control Valve, Air-to-Close (ATC), bench range 3-10 psi, Cv=4.0, brand Fisher.

Installation Considerations

Before installing a control valve it is necessary to ensure that the size, pressure rating, materials and end connections are all suitable for the conditions under which the valve is expected to work.

The control valve must be installed to ensure the correct direction of flow of the medium passing through the valve.

Control valves should generally be installed in horizontal pipelines with the spindle/stem vertical.


TE11(STATION 4)

Specifications Thermocouple Type K

Process Conditions

Liquid and steam process of high temperature with velocity less than 300 ft / sec. Process does not involve vibrations and no extreme operations/hazardous area.

Physical location

Located closed to heat source to maximize the temperature reading of processMounted inside the vessel for direct contact with the process

Device performance

Temperature range = 0 to 100°CSensitivity = 41 µV/°CNickel part of the probe is magnetic so its show abrupt variation in emf above temperature around 50 deg C


FI13(STATION 4)

SpecificationsRotameter (Variable Area Flowmeter)Pmax / Tmax = 4 bar / 55 deg C

Process Conditions

Gas Flow Process of high temperature with velocity less than 300 ft / sec. Process does not involve vibrations and noisy operations/hazardous area. Control gas flow, clean process Non corrosive air process

Physical location

Flow meter must be install verticallyThe area of installation also affects the selection process. Consider the layout and piping details prior to the choice of a flow meter. Type and size of flow meter that satisfies your conditions.Vibrations and magnetic fields in the application area could also affect flow meter readings.

Device performance

Accuracy = +/- 0.5% Fast responseRepeatability


Orifice(STATION 4)

SpecificationsOrifice plate with flange, D=25.4mm, d=17.16mm, concentric bore type with square edge.

Process Conditions

Heat exchanger flow pipe carrying non-corrosive, low viscosity vapor/gas/liquid with temperature above 60 deg C.

Physical location

The service area should provide a way for the plate to be removed, inspected and if necessary replaced.Must be easily accessed/maintained for diff. pressure sensed through the taps and recorded by a secondary element.Must comply to straight requirement of 26D upstream and 7D downstream to get correct flow profile (ISO5167)

Device performance

Made of “zero corrosion” materials, usually stainless steel, Monel or alloys.Suitable where head pressure loss is not critical.


Orifice(STATION 2)

SpecificationsOrifice plate with flange, D=25.4mm, d=17.16mm, concentric bore type with square edge.

Installation Considerations & precautions

The plates must be flat, clean, & hold firmly in the center of the line at 90 deg to gas flow, so that all gas passes through the orifice. Upstream edge must be sharp.Installation of fittings come equipped with taps at 1 inch from each side of plate.

Choice of pressure tap locations depend on flow conditions, pipe size and accuracy needed. In this type of process, flange taps are used due to small pipe diameter.

Meter tubes and fittings are often installed slightly higher so that the tap holes are facing upward in situations where free liquids in gas from heat exchanger can accumulate at plate. Therefore it will drain back.


PG92(STATION 3)

SpecificationsPressure Gauge (Bourdon type)Meas. Range 0 – 30 psi / 0 – 2.4 bar

Process Conditions

Gas is flown into closed pressurized storage tank containing compressible non-corrosive, non-explosive medium (gas/vapor). Process is non-noisy, not subject to vibrations and extreme conditions.

Physical location

Located on top, in direct contact with the tank where the head pressure of condensable vapor can be measured.The gauge can be clearly viewed by operator (height of about 1.8m)

Device performance

Simple, rugged and low cost.Range from 0-30 psi suitable to storage tank design pressure limit .Tolerable inaccuracy of < 2% of span.Easily maintained, calibrated and isolated for service purpose.


PG92(STATION 3)

SpecificationsPressure Gauge (Bourdon type)Meas. Range 0 – 30 psi / 0 – 2.4 bar


Where possible, a bypass / shut-off is done to isolate the gauge from the process.The gauge is then attached to the dead weight tester.Then, a constant pressure is produced when a weight is put while the pressure gauge is tuned .Make sure that the reading of the gauge is proportional to the applied pressure as seen by the plunger scale, otherwise needle adjustment is needed .

Diagram:Using a dead weight tester to calibratepressure gauge.

SELECTION, CALIBRATION & INSTALLATION

Selection of instrumentation is important in plant management especially during start-up and commissioning.

Therefore, it is essential for instrument engineer to carefully select the most suitable, technically/economically to achieve optimum process quality.

Every selection done need to be documented properly for further revision and updates.

Operator also need to know the basic of instrument calibration together with installation.

Conclusion

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Documents

reference temperature

temperature resistance

tank temperature

temperature source

broad temperature span

large temperature coefficient

gauge stem

calibration control