Since last post considerable time was lapsed I could not deliver any post due to illness. I hope i will resume to share my experience of professional life with all of you.
There are four instruments generally used any process plant as basic instrument since invent of such instruments. Therefore basic specification is given below for procuring instrument at site if required. The instruments are Pressure gauge and Differential pressure gauge , Temperature gauges , Resistance temperature detector, Thermocouples. Different and details of their principle can be available in a book therefore need not to be discussed here. I request reader to scan through the leaflet of the manufacturer and understand the applicability. I like to mention please be careful about the connection ( i.e thread available in the instrument and process). Most of the time it is observed mismatch between the two and land into problem during installation which may require one more piece to match both.
Specification for Pressure Gauge and Differential Pressure Gauges
Type :Bourdon
/Bellow /Diaphragm
Sensing
Element material : AISI
316 SS
Movement
Material : AISI
304 SS
Case
Material :
Die cast Aluminium, stove enameled ,black finish
Threaded
bezel Ring ,clear glass cover as per
NEMA
4x
Dial Size :
Generally 150 mm, other sizes are
100mm,
250
mm as specified.
Scale Size : Black
lettering on white background in 270 Degree
arc.
Range
Selection :
Normal process pressure 70 per cent of Range.
Over range
Protection :12% of maximum range by internal stop. External
Stop
at Zero.
Adjustment : External
micrometer screw for zero adjustment .
Internal
micrometer screw for range adjustment
Element connection
Brazing for range
below 40 kg/ cm2
Argon
welding for range above 40kg/cm2.
Process
Connection M20x1.5
(M) { bottom or back}
Performance Accuracy :+/-
1.0 % or less of span. 80deg ambient
Safety
feature Blow
out disc at the back.
Applicable
standard IS:3624-1966
Specification for local
Temperature gauges (Capillary)
Type Mercury
filled
Sensing
Element material Bourdon- AISI
316 ss/ chrome moly
Bulb and
capillary material ,dia AISI 316 ss /12
mm
Capillary
armouring Solid drawn
316SS with SS armour
Movement
material 304 SS
Thermowell
connection M33x2
Case
material Die
cast aluminium , black finished.
Dial Size 150
mm
Scale Black
lettering with white back ground
Mounting Surface
Over range protection 125% FSD
Instrument
Connection Bottom /M20X1.5
Accuracy +/- 1%
of full scale ,Zero adjustment
Enclosure
class IP 55
Capillary
Length 5 M
Accessories Thermowell
( weldable or screwed as per
ASMEPTC code.
Specification for
Resistance Temperature Detector
Platinum / Copper
Type : Platinum /
Copper.
Resistance 100 ohm at 0 deg C /
53 ohm at 0 deg C
Base wound on
ceramic
Wiring 3 wire system
Protecting Tube 8mm/316
Ss seamless , filling MgO ( purity 99.4%)
Head NEMA
4X/IP55, Die cast aluminium, Brass Terminal
Silver
plated , cable gland with grommet ,
Terminal
Head
cover with SS chain and suitable gasket
Accessories Connection , flanges ,
thermowell , conduit etc.
Simplex /
Duplex Duplex.
Standard DIN 43760
Response Time 30
secs
Accuracy 0.1 at 0 deg C
Insulation
Resistance 10M ohm at 250V Dc at 27deg C and 600deg C
Specification for
thermocouples
Type Cr.
Al ( popularly known as K-type.)
Wire gauge 16 AWG
Standard ANSI-C96-1- 1975
Protecting Tube 6 mm OD, 316 SS Seamless , MgO filling
Loading Spring loaded.
Head IP 55 ,
Die –cast aluminium , Brass Silver plated
Connector , cable gland, head cover with SS
Chain
and suitable gasket.
Accessories Thermowell , flanges
,fittings etc as per requirement
Type of
grounding Ungrounded/grounded
as per requirement
Response
time within six
seconds
Accuracy Standard ISA
All the specification given above is typical can be changed according to process requirement. RTD generally used are platinum RTD or copper RTD. In BHEL sets copper RTD are used mostly in generator stator and stator water circuit and blance all the places it is platinum RTD.
CRT chart is given and other chart will be given as soon as it is available with me.
continued to PART -III
