# In-04-05

Document Sample

```					Abu Dhabi National Oil Co. ADNOC Technical Institute

INSTRUMENTATION
INSTRUMENTATION II

UNIT 5

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 1 OF 13 IN-04-05

UNITS IN THIS COURSE

UNIT 1

MEASUREMENT OF TEMPERATURE

UNIT 2

TEMPERATURE TRANSMITTER

UNIT 3

THE CONTROLLER

UNIT 4

VALVES AND ACTUATOR

UNIT 5

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 2 OF 13 IN-04-05

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 3 OF 13 IN-04-05

ADNOC TECHNICAL INSTITUTE PRACTICAL TASK 1 CALIBRATING AN INDUSTRIAL THERMOMETER INTRODUCTION Most industrial thermometers cannot be calibrated. All you can do is check that they are reasonably correct. This is true for mercury in glass and bimetal strip thermometers. However, some of the "filled system" types can be calibrated for zero and span. You can calibrate for zero by adjusting the pointer. You can calibrate for span by adjusting the Bourdon tube linkage, in the same way as with a pressure gauge. TEMPERATURE STANDARDS. The basic standards for all temperature calibration are: 1) The ice point; ice melting in distilled water at a standard pressure of 101 325 Pa. This is 00 C or 32O F. 2) The boiling point of distilled water at a standard pressure of 101 325 Pa. This is 100C or 212F. Other fixed points for temperatures outside this range are internationally agreed. This is called the International Practical Temperature Scale (IPTS). A few examples of these points are given below: Boiling point of oxygen The freezing point of mercury The freezing point of zinc The freezing point of silver The freezing point of gold = = = = = -182.9620 C -38.8620 C 419.580C 961.930C 1064.430C

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 4 OF 13 IN-04-05

ADNOC TECHNICAL INSTITUTE You will probably never see any calibrations carried out using these standards. The calibration equipment in the instrument workshop is It is calibrated against the above calibrated when it is manufactured.

standards and given a calibration certificate which shows its accuracy. When you get it from the manufacturer your equipment should be correct. A good instrument workshop sends its calibration equipment for recalibration every year. Then a new calibration certificate is given. The most common industrial standard thermometer is the platinum PT 100 . This should be accurate to 0.10 C over the range 15 to 10000 C. This thermometer is fitted into a temperature bath (usually sand filled or solid block). The electrical heater for the temperature bath is controlled by the PT 100 . The temperature of the bath is given on a digital read out. An example of a workshop temperature calibration bath is shown in Figure PT1. The AMETEK dry block calibrator has a range of -40 to 1230C and an accuracy of 0.50C.

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 5 OF 13 IN-04-05

Figure PT-1 Ametek Dry Block Calibrator
CALIBRATION PROCEDURE The ATI does not have a modern temperature calibration bath. The

following calibration is done using a "sand filled" temperature bath which does not keep such a steady temperature. The standard temperature is set using a semi-standard mercury in glass thermometer. Remember to use the immersion line for correct calibration. used as the standard 00C. An ice/water mixture is

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 6 OF 13 IN-04-05

ADNOC TECHNICAL INSTITUTE A layout of the calibration procedure is shown in Figure PT-2.

SEMI-STANDARD MERCURY IN GLASS

THERMOMETER UNDER CALIBRATION

FILLED SYSTEM IMMERSION LINE ICE

SAND AIR SUPPLY (5 PSI) SET TEMPERATURE ZERO
0

DISTILLED WATER

C

Figure PT-2 Basic Thermometer Calibration
CALIBRATION STEPS 1) Place the thermometer which you are testing in the ice/water mixture. It should read zero on the scale. If the thermometer is the filled system/Bourdon tube type, adjust the pointer to read zero. 2) Place the thermometer which you are testing in the temperature bath and adjust the set temperature so that you get the maximum indication on the thermometer dial. indication point. 3) Non adjustable thermometers are OK if they are within 20C. 4) The filled system types can, with care, be set to an accuracy of about 10C. Note: The above calibration procedure is the same using a modern temperature bath, but the ice is not needed. Also the quick response of the modern bath allows you to plot a graph to show linearity. The CDC bath needs an air supply. The air flows through the sand so that the temperature is the same in all parts of the sand bath.
PRACTICAL TASKS DATE OF ISSUE 8-DEC-09 PAGE 7 OF 13 IN-04-05

If the thermometer is of the

40F or

ADNOC TECHNICAL INSTITUTE RESISTANCE TEMPERATURE DETECTORS (RTDs) AND THERMOCOUPLES (T/C) There is no way you can calibrate an RTD or T/C. If the RTD has a

resistance reading (not open or short circuit) it is good. If the T/C has a resistance (very small) it is good. Conversion tables are used to change the measured resistance of the RTD into a temperature reading. Conversion tables are also used to change the mV readings of the T/C into a temperature reading. Modern RTD and T/C detectors will provide a direct reading in 0C or 0F so you don't need conversion tables. calibrator is shown below. compensation. model 4610T. following: T/C Type J,K,T,E,R,B N,G and D. RTD Platinum PT 100  and Copper 10  with either a 2, 3 or 4 wire configuration. The accuracy is better than 0.50C. A typical RTD and T/C detectorAll good calibrators have full ambient (cold

junction) compensation so you don't need an "ice bath" for cold junction Figure PT-3 shows a typical all purpose calibrator; Beta It will measure and display in either 0C or 0F for the

Figure PT-3 Beta Temperature Calibrator

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 8 OF 13 IN-04-05

ADNOC TECHNICAL INSTITUTE PRACTICAL TASK 2 CALIBRATING A TEMPERATURE TRANSMITTER INTRODUCTION There are many methods for calibrating a temperature transmitter. The simple method uses a temperature bath, a filled system sensor, and a pneumatic transmitter. Modern electronic transmitters are normally calibrated using a temperature calibrator which can measure either mV for a T/C or ohms for the RTD. It can also produce a voltage or resistance value to represent the T/C or RTD sensor. In this way the transmitter can be calibrated without the use of a temperature bath. temperature transmitter. CALIBRATING A FILLED SYSTEM PNEUMATIC TRANSMITTER The following procedures show some of the usual methods used to calibrate a

TRANS MITTER OUTPUT AIR SUPPLY 20 psi

0-20 psi TEST GAUGE

CAPILLARY

TEST THERMOMETER SENSOR

TEMPERATURE BATH

SET TEMPERATURE

Figure PT-4 Calibrating a Filled System Pneumatic Pressure Transmitter

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 9 OF 13 IN-04-05

ADNOC TECHNICAL INSTITUTE Figure PT-4 shows the layout required to calibrate a filled system, pneumatic, pressure transmitter. CALIBRATION PROCEDURE 1) 2) The calibrated range of the transmitter will be given by the instructor. Adjust the temperature bath to the minimum value of the transmitter range. 3) When the temperature of the bath is steady adjust the reference adjustment on the elevation spring so that you get 3 psi or 0.2 bar on the output test gauge. 4) Adjust the temperature bath to the maximum value of the transmitter range. 5) When the temperature of the bath is steady, adjust the feedback bellows so that you get 15 psi or 1 bar on the output test gauge. 6) Repeat steps 2 through 5 until the outputs are correct at both temperatures. 7) The output should be linear between 3 and 15 psi (0.2-1 bar) and no more calibration is needed. The above procedure is a simple summary of the manufacturer's instruction manual. You will need this manual to find the components and to adjust the feedback bellows.

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 10 OF 13 IN-04-05

ADNOC TECHNICAL INSTITUTE CALIBRATING AN ELECTRICAL/ELECTRONIC TEMPERATURE TRANSMITTER INTRODUCTION Manufacturers of electrical/electronic temperature transmitters produce these transmitters for most types of T/C's and RTD's. The electronic board inside the housing is changed to suit a particular T/C (e.g. type J,K etc.) or RTD (e.g. PT 100  or copper 10  etc.). The transmitter has a special number to indicate what it does. before calibration can be done. This must be checked in the manual The CDC instrument workshop has

different examples of the Rosemount model 444 Alphaline temperature transmitter. This transmitter is used a lot by ADNOC and the operating companies. The basic calibration procedures done on the model 444 are the same for any type of temperature transmitter. However, because of small differences in design the manufacturer's manual must be used in all cases. CALIBRATION PROCEDURE The calibration procedure must be done using the manufacturer's manual. The instructor will show you how to find out what type of transmitter is to be calibrated. This is complicated and will only apply to the Rosemount model 444. Other types, used on job site, will have similar complicated manuals.

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 11 OF 13 IN-04-05

ADNOC TECHNICAL INSTITUTE However, the basic calibration of a temperature transmitter is much the same and the same test equipment is used. There are two basic layouts.  When the transmitter is of the T/C type.

DVM

–
TEST

+
STANDARD RESISTOR

+ –
POWER SUPPLY

T/C CALIBRATOR

+
DVM

–

Figure PT-5 Calibration of a T/C Transmitter
Figure PT-5 shows a block layout for the calibration of a T/C transmitter. The T/C calibrator simulates the T/C temperature by sending a mV signal which corresponds to the T/C type (J, K, N etc.). The DVM is usually connected across the test position. The zero and span are adjusted to give a 4-20mA output signal corresponding to the T/C sensor range (eg. 100400°C). Note : Sometimes it is better to add your own standard resistor in series with the output. The DVM is then placed across this to measure the 4-20mA. A typical standard resistor is of the wire wound type (eg. 10  ±0.1%). This produces a 40mV to 200mV signal.

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 12 OF 13 IN-04-05

ADNOC TECHNICAL INSTITUTE  When the transmitter is of the RTD type

DVM

–

+
STANDARD RESISTOR

+ –
POWER SUPPLY

+
DVM

–

Figure PT-6 Calibration of RTD Temperature Transmitter
Figure PT-6 shows the block layout for the calibration of an RTD temperature transmitter. The input RTD resistance value for the temperature comes from a decade box (standard variable resistor). The output 4-20mA is measured by using either the test position or a standard resistor. The zero is adjusted to give 4mA for the minimum temperature set by the decade box. The span is adjusted to give 20mA for the maximum temperature set by the decade box. Note : Modern calibrators produce a resistance output so a decade box is not required. The calibrator is connected to the transmitter. In this case a three wire system is used. The calibrator is then programmed to give the required RTD resistance values.

PRACTICAL TASKS DATE OF ISSUE 8-DEC-09

PAGE 13 OF 13 IN-04-05

```
DOCUMENT INFO
Shared By:
Categories:
Stats:
 views: 65 posted: 12/8/2009 language: English pages: 13
Description: Instrumentation Course