About kishore karuppaswamy

Iam Btech having experience in saudi aramco as instrument engineer

Tips and tricks in field instrumentation


  1. For RTD Pt 100 measurement,measure  the resistance across the white and common terminal, then the temperature can be calculated simply by

    Temp=(resistance measured across terminal minus 100)/0.385  or (resistance measured across terminal minus 100)multiplied by 2.6

for example

if the resistance across white and red terminal is 126 ohm, then

the temperature measured is 26/0.385=67.53 degree centigrade or 26 multiplied by 2.6


 This follow the same eqn, R=Rₒ(1+αT) remember that this is only applicable for PT 100 not other types

  1. For calibration of -100 mmH2O to -10 mmH20 range capillary type using pressure pump not vacuum pump

The values for 25%,50%,75%,100% are as follows:

0%————-     -100 mm h2o

25%———–      -77.5 mm h2o

50%——–          -55 mm h2o

75%———         -32.5 mm h2o

100%——           -10 mm h2o

First find the Span=URV-LRV=-10+100=90 

Then divide this by 4 as we are  calibrating for 4 values namely 25%,50%,75%,100%

i.e. 90/4=22.5

then the 4 points can be calculated as follows

0%(4ma)————-     0 mm h2o i. e LP  and HP open to atmosphere

25%(8ma)———–      -0+22.5=22.5 mm h2o (apply 22.5mmh2o to HP side not LP here LP is open to atmosphere.)

50%(12ma)——–    22.5+22.5=44 mm h2o (apply 44mmh2o to HP side not LP)

75%(16ma)———         44+22.5=67.5 mm h2o (apply 67.5 mmh2o to HP side not LP)

100%(20 ma)——           67.5+22.5=90 mm h2o (apply 90 mmh2o to HP side not LP)

  1. Calculation of flow m3/hr from differential pressure  values mm h20 if both ranges are known:

We know that the flow equation is related as follows


Here Q is the rate of flow: k is the Bernoulli’s constant;  and ∆p is the differential pressure

Consider for instance the D.P. transmitter is of range 0 to 120 mm H2O and the DCS range of

0 to 1500 m3/hr

Then the next step is to find the Bernoulli’s constant

i.e. Q=k√∆p

1500=k√120 (here we consider span URV values to find Bernoulli’s constant)



Once we get Bernoulli’s constant we can calculate any flow rate if we know the D.P. 

For e.g.

If differential pressure is 90 mmH2O

Q=k√∆p becomes


   = 136.936*9.486 = 1298.9 m3/hr

Thus we can calculate any flow rate if we know the transmitter and DCS range.

4.For K type thermocouple (Chromel alumel) if the mV measured across yellow(positive) and red (negative) is x,then the temperature can be calculated as follows

Temperature=x/0.0397(millivolt measured divided by 0.0397) or x *25.2 (millivolt multiplied by 25.2)

for example if we measure the mV value across yellow and red terminal using a multimeter and found to be 0.397 then temperature can be calulated by

temperature=(0.397/0.0397)=10 degree centigrade or (0.397*25.2)=10 degree centigrade

6.calibration checking of capillary type LT if you dont have any instruments for checking

Suppose that a capillary type LT is mounted on a tank having range of -1200mmh2o as LRV and URV -60 mmh2o and you need to check whether the transmitter is Ok

We know that the transmitter is mounted with HP side to high pressure side and LP tapping to low pressure side,Firstly isolate the process line,vent and drain the process inorder to release any trapped pressure inside the flange.the transmitter will show 0% reading ie(-1200mmh2o),

Now measure the tap to tap length and mark the corresponding 25%,50%,75% and 100% level .Remove the LP flange of the transmitter(with HP flange of capillary intact) and keep it near(parallel) to HP tapping, the transmitter will show 100%.Now lift the LP capillary flange to  25% above from the HP tapping (where we marked before as 25%),now the transmitter will show 75% (not 25%)

Next keep the transmitter LP capillary flange at 50% marking the transmitter will show 50% reading.Similarly when we place at 75% the transmitter will be showing 25%

Finally if we place at 100% marking the transmitter should show 0% that is -60mmh2o

Calibration,theory and initialization of GWR level transmitter Rosemount 5300 and Ktek 5100



and the blanking distance or blocking distance is used to ignore an extended nozzle that would otherwise cause a reflected signal at the top of the probe and result in a high level reading even when no product is in the vessel

and the Level offset is used to correct the level output of the transmitter to match the actual level in your tank or vessel.There are two cases when Level Offset can be used. One is to accommodate for a unmeasurable length at the bottom of the probe (a negative offset) The other is to accommodate for the length of the probe being shorter than the actual depth of the tank (a positive offset).

seems confusing but I will make it clear, if physical dip tape  or gauge measures 1200 mmwc and transmitter is showing 1000 then put level offset as +200 mmwc

and if physical dip tape  or gauge measures 1200 mmwc and actual  level is 1400 mmwc then put level offset as -200mmwc then the transmitter display will show 1400-200=1200 mmwc which matches with physical reading……………..means this is a trick provided by the company to match physical reading with transmitter reading



Calibration and Initialization of Electronic Remote Seal level transmitter -Rosemount 3051ERS


ersInitial setting of transmitter:

After installation of the transmitter, measure the tap to tap length of the H.P. side and L.P. side, here consider the level to be measured=the tap to tap measured length be 9000 mm, the LRV and URV can be calculated as follows

LRV=Value when the tank is filled with upper liquid of lower density=height of the tap to tap measurement*S.G. of upper liquid=9000*0.85=7650

URV=value when the tank is filled with lower liquid of higher density=Tap to tap measurement*S.G of the lower liquid=9000*1=9000

Calibration of the LT:

Fill the tank with water or the liquid with higher density then the transmitter should show 100%

Next fill the tank with liquid of lower density then the transmitter should show 0%

Calibration and initialization of Wet leg impulse tube Rosemount 3051CD series LT

Calibration and Initialization of Impulse tube type Level Transmitter Rosemount 3051CD:


Initial setting and calibration for water tank (here specific gravity =1)

Initial setting:

Take tap to tap measurement, for example if tap to tap measurement is 600mm then put

LRV=negative of tap to tap reading= -600mmWC    {negative value because after filling water on LP side the reading will be a negative value}

Put URV=0mmWC

Calibration of LT

here we are doing only zero checking; fill the impulse tube with water on both sides the transmitter reading should show zero reading i.e. -600mmWCor 0% level then the transmitter is O.K.

Initialization and calibration of tank having liquid of specific gravity other than water and impulse tube filled with liquid like that of glycol:


Initial setting:

take tap to tap measurement for e.g. if tap to tap measurement is 600mm and we are filling with glycol of 0.86 s.g. then

LRV=negative of tap to tap reading *s.g. of liquid inside impulse tube



and URV because of liquid inside vessel of s.g. 0.92is

URV=  LRV+ level(height) to be measured*s.g. of liquid inside vessel

= -516+(0.92*600)


=36 mm WC

Calibration (Zero checking):

fill the impulse line with glycol on both LP and HP side then the transmitter should show LRV=-516mmWC and 0% level


LRV= -600*1= -600mmWC


= -600+(600*1)

= -600+600

= 0 mmWC


N.B.  Calibration and initialization of DP type level follows a simple rule

LRV= level and property of liquid in impulse tube acting on LP side of LT

URV=LRV+level and property of liquid inside vessel acting on HP or

Feeling confused !!!!!!!!!!!!!!!!

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