Pressure Measurement

CDB 3062 CHEMICAL ENGINEERING LAB 3 MAY 2016

GROUP

: 03

DATE

: 20th June 2016

EXPERIMENT

: PRESSURE MEASUREMENT

GROUP MEMBERS

: HUSSIEN SAQAFF AHMED ALKAFF NORANISAH BINTI JAMIAN NGOT MOU MADUT MOU NURFARAH HUSNA BINTI MOHD HANAFIAH NAZRIL DANIEL BIN ABDULLAH

19496 19339 20487 19351 18996

1

Table of Contents SUMMARY............................................................................................................... 3 THEORY.................................................................................................................. 4 PROBLEM STATEMENT............................................................................................ 5 OBJECTIVES............................................................................................................ 5 PROCEDURE........................................................................................................... 6 Start-up Procedure.......................................................................................... 6 Method 1: Draft Calibration of EJA430A Pressure Transmitter..........................6 Method 2: Hysteresis....................................................................................... 6 Method 3: Five Point Calibration......................................................................7 RESULTS................................................................................................................. 7 DISCUSSION........................................................................................................... 9 ERRORS AND RECOMMENDATION........................................................................10 CONCLUSION....................................................................................................... 10 REFERENCES........................................................................................................ 10 REVIEW QUESTIONS............................................................................................. 11 APPENDIX............................................................................................................. 13

2

SUMMARY Pressure, which is defined as force per unit area is usually more convenient to be used rather than force in describing the influences upon fluid behaviour. The standard unit for pressure is the Pascal, which also stands for Newton per square meter. The pressure for an object sitting on a surface is the force pressing on the surface, which is the weight of the object. However, in different scenario the object might have different area in contact with the surface and therefore exert a different type of force or pressure. Many techniques have been developed for the measurement of pressure and vacuum. In this experiment, we are trying to determine of Test Uncertainty Ratio (TUR) for the EJA430A pressure transmitter, to draft UUT Calibration of EJA430A Pressure Transmitters, to verify the resolution of the pressure transmitters, to determine the hysteresis of the pressure measurement devices, and to obtain five point calibrations of pressure transmitters in different parts of the experiment. The experiment is being conducted in three different parts, which requires different types of readings to be taken from the equipment used. After all the experiment had been undergone, we are required to calculate the final results as well as to plot the hysteresis plot for the pressure measurement.

3

THEORY Pressure is defined as force per unit area that a fluid exerts on its surroundings which can be described as either static or dynamic. The pressure in cases with no motion is static pressure. Examples of static pressure include the pressure of the air inside a balloon or water inside a basin. Often, the motion of a fluid changes the force applied to its surroundings. For example, say the pressure of water in a hose with the nozzle closed is 40 pounds per square inch (force per unit area). If you open the nozzle, the pressure drops to a lower value as you pour out water. A thorough pressure measurement must note the circumstances under which it is made. Many factors including flow, compressibility of the fluid, and external forces can affect pressure. A pressure measurement can further be described by the type of measurement being performed. The three methods for measuring pressure are absolute, gauge, and differential. Absolute pressure is referenced to the pressure in a vacuum, whereas gauge and differential pressures are referenced to another pressure such as the ambient atmospheric pressure or pressure in an adjacent vessel. The absolute measurement method is relative to the static pressure in a vacuum. The pressure being measured is acted upon by atmospheric pressure in addition to the pressure of interest. Therefore, absolute pressure measurement includes the effects of atmospheric pressure. This type of measurement is wellsuited for atmospheric pressures such as those used in altimeters or vacuum pressures. Next is gauge pressure. Gauge pressure is measured relative to ambient atmospheric pressure. This means that both the reference and the pressure of interest are acted upon by atmospheric pressures. Therefore, gauge pressure measurement excludes the effects of atmospheric pressure. These types of measurements include tire pressure and blood pressure measurements. Moving on, differential pressure is similar to gauge pressure in some way; however, the reference is another pressure point in the system rather than the ambient atmospheric pressure. This method can be used to maintain relative pressure between two vessels such as a compressor tank and an associated feed line.

4

PROBLEM STATEMENT The pressure is a measurement of force exerted per unit area, which is often measured through Pressure transmitter or pressure sensor that acts as transducer, thus generating a signal as a function of the pressure indicated. There are 5 different experimental errors that are needed to be performed, in order to study the pressure measurement device in this experiment. In the first part of the experiment, MSU need to be selected based on the Test Uncertainty ratio and Draft calibration. Following that method, the resolutions of instrument need to be verified and observe. The resolution refers to the smallest value of the variable that can be differentiated by the instrument. The phenomenon that is caused by stick-slip friction is called Hysteresis, which is backlash in gears and saturation in electronic devices and that is one of the experimental errors that need to be observed for the pressure measurement devices. The five-point calibration of the instrument, which is done in the last part of the experiment, is a method used for periodic calibrating of the process instrument.

OBJECTIVES The objectives of this experiment are:     

To determine the Test Uncertainty Ratio (TUR) for the EJA430A pressure transmitter To draft Units Under Test (UUT) Calibration of EJA430A Pressure Transmitters. To verify of the resolution of pressure transmitters or pressure sensor. To determine the hysteresis of the pressure measurement devices. To obtain five points calibration curve of pressure transmitters (EJA 430A pressure transmitter)

5

PROCEDURE Start-up Procedure

Figure 1: Experimental Setup for Draft UUT calibration EJA430A Pressure Transmitter For this part of the experiment, there are two approaches; the first one is by fixing the value of UUT, and change the value of MSU to get the desired UUT. For second approach, we change the value of MSU, and see how it effect on the UUT value. 1. EJA430A Pressure Transmitter range is confirmed to be set to 0 to 200 kPa. 2. UM330 Digital Indicator input range is confirmed to be set to 0 to 200 kPa. 3. Air supply to MC100 Pneumatic Pressure Standard is confirmed to be set to 280 kPa before connection. 4. The equipment is connected as shown in Figure 1 with EJA430A pressure transmitter as the UUT Method 1: Draft Calibration of EJA430A Pressure Transmitter 1. The value of the MTU was adjusted to 0 KPa. 2. The value of UUT is recorded. 3. The tolerance of UUT is calculated. 4. The experiment is repeated with the MTU values ranging from 0 KPa to 200 KPa with the increment of 20 KPa. Method 2: Hysteresis 1. The pressure transmitter is set at 0 KPa. 2. The value of MTU is adjusted so that so that the transmitter reaches the desired value. 3. The value of MT220 digital manometer is recorded (actual UUT reading). The desired UUT reading is the whole number of the value. 4. The experiment is repeated with the transmitter values ranging from 0 KPa to 200 KPa with the increment of 20 KPa.

6

Method 3: Five Point Calibration 1. The Pneumatic Pressure Standard is adjusted so that the UUT reads the first point. In the case of the pressure transmitter the first point on the output is 4 mA which corresponds to an input of 0 kPa. 2. The value of MT220 digital manometer is recorded (actual UUT reading). The desired UUT reading is the whole number of the value. 3. The experiment is repeated with the UUT values of 50 KPa, 100 KPa, 150 KPa and 200 KPa.

RESULTS

Graph 1 UUT reading versus MSU reading

Graph 2.1 UUT readings vs MSU Reading for increasing MSU Applied Value (kPa) and UUT Output (mA) 7

Graph 2.2 UUT readings vs MSU Reading for increasing MSU Applied Value (kPa) and UUT Output (mA)

Graph 3 Actual UUT Output (mA) vs MSU Applied (kPa) for thefive Points Calibration of EJA430A Pressure Transmitter.

8

DISCUSSION Our discussion of this experiment covers the draft Calibration of EJA430A Pressure Transmitter by Method one, hysteresis in EJA430A Pressure Transmitter as well as five Point Calibration of EJA430A Pressure Transmitter. According to the graph 1 above, we observed that the UUT readings versus MSU readings are directly proportional to each other as shown by the linear graph line. Besides; the linearity of these two reads is brought about by the uniform or constant tolerance of 0.1 kPa from 20 th and 180th readings. And 0.0 kPa in both initial and last readings. Therefore the unit under test is said to be perfect since its tolerance with measured standard units is constant and small too. Furthermore; hysteresis is the phenomenon in instruments in which the set values of the input in the instrument at an increasing value produces different output at the same instruments if the input is set at decreasing value. However we observed a linear line with the slope of 0.080 and constant of 4.0291 on graph 2:1 for the increasing UUT readings against MSU readings. On the other hand; graph 2:2 of the same hysteresis under the state of decreasing set values, we observed a linear graph of 0.08 slope and constant of 4.0364. Nevertheless the differences between the constant of the two graphs are due to the lagging process effect of decreasing and increasing values, hence hysteresis. On the other hand; on the five Point Calibration of EJA430A Pressure Transmitter graph 3, we obtained a linear graph with a slope of 0.0801 and a constant of 4.028. However the different between its slope and the other above graphs is due to its few points chosen only. This is observed on the error columns in table 3. The trend of the error showed that error decreases as the reading increases. For instant at zero reading the error is 0.750 % and at 100 reading it is 0.25 %. So the error decreases as the reading increases.

9

ERRORS AND RECOMMENDATION Errors 1. The MSU and UUT readings are slightly different from the fixed values when conducting the experiment. 2. The experiment was conducted in open air condition for which temperature of surroundings might affect the resistance of wires and give slightly different error. 3. There are some malfunctions that cannot be avoided due to the defected electronic device since the device has been used in experiment for many times. Recommendations 1. To get an accurate results, the experiment can be improved by repeating the experiment and obtain the average value. 2. Before recording a value, the indicator needs to be stabilized before the value is taken. 3. Recheck the wires so that they are connected correctly and properly to all devices.

CONCLUSION In conclusion, we managed to conduct the experiment regarding Calibration of EJA430A Pressure Transmitter by Method one, hysteresis in EJA430A Pressure Transmitter as well as five Point Calibration of EJA430A Pressure Transmitter. In this experiment, there is selection of the MSU based on the Test Uncertainty Ratio, Draft Calibration, and Resolution of instrument, hysteresis of the instrument and five-point calibration of the instrument. Three different types of instruments, that is, a pressure gauge which is an analogue instrument, digital manometer as an example of digital instrument and two different types of electronic transmitters have been studied.

REFERENCES Chemical Engineering Lab III Lab Manual. (n.d.). Pressure Measurement. Morris, K. A. (n.d). What is Hysteresis?. https://uwaterloo.ca/applied-mathematics/sites/ca.appliedmathematics/files/uploads/files/morris_hysteresis_final.pdf

Retrieved

from

10

National Instruments. (2016). Pressure Measurement Overview. Retrieved from http://hyperphysics.phy-astr.gsu.edu/hbase/press.html Retrieved from http://www.ni.com/white-paper/13034/en/ User’s Manual. Model EJA310A, EJA430A and EJA440A Absolute Pressure and Gauge Pressure Transmitters. Retrieved 2 June 2016 from http://webmaterial3.yokogawa.com/ IM01C21D01-01EN_012.pdf

REVIEW QUESTIONS 1. Derive an expression for the pneumatic system assuming suitable equations for gas flow? Rate of change of mass:

Since (dV/dt)=(dV/dp)(dp/dt) an, for ideal gas, pV=mRT, then

Where R is the gas constant and T is temperature, assumed to be constant on Kelvin scale. Thus:

2. How do we define the resistance and capacitance in such a system? Pneumatic Resistance:

Where, m: mass of the gas; P1-P2: pressure difference; R: resistance Pneumatic capacitance (C) is due to compressibility of the gas in some volume. Based on the equation from question 1, the pneumatic capacitance due to change in container C1 is defined as:

And for the pneumatic equation due to compressibility of gas at C2:

Hence

3. Draw an electrical analogue of the system.

11

4. What is transmitter? Transmitters are devices that are used to transmit data as radio waves in a specific band of the electromagnetic spectrum in order to fulfil a specific communication need; it can be for voice or for general data. In order to do this, a transmitter takes energy from a power source and transforms this into a radio frequency alternating current that changes direction millions to billions of times per second depending on the band that the transmitter needs to send in. When this rapidly changing energy is directed through a conductor, such as an antenna, electromagnetic or radio waves are radiated outwards to be received by another antenna that is connected to a receiver that reverses the process to come up with the actual message or data. 5. What is the standard output from the transmitters’ studies in the experiment? The standard output from the transmitter that used in this experiment is 420mA. Since a 4-20mA signal is least affected by electrical noise and resistance in the signal wires, these transducers are best used when the signal must be transmitted long distances. 6. What is resolution? Resolution is the minimum pressure change detected by the sensor. When referring to the resolution of a bottom whole pressure gauge, it is important to account for the associated electronics, because the gauge is always used in series with the electronics. Thus, the resolution of the measurement is the lower of the resolution of the gauge and its electronics. Another important consideration is that the resolution must be evaluated with respect to a specific sampling rate, because an increase of the sampling rate will worsen the resolution. The electronic noise of strain-gauge transducers is often acted as the major factor affecting resolution. Mechanically induced noise may further limit gauge resolution because some gauges behave like microphones or accelerometers. This effect may be significant during tests when there is fluid or tool movement down hole.

12

APPENDIX Table 1: Draft Calibration of EJA430A Pressure Transmitter by Method 1 No 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Reading of kPa (UUT) 0.0 20.0 40.0 60.0 80.0 100.0 120.0 140.0 160.0 180.0 200.0

Tolerance of kPa 0.0 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.0

MSU Reading 0.0 19.9 39.9 59.9 79.9 99.9 119.9 139.9 159.9 179.9 200.0

Table 2: Hysteresis in EJA430A Pressure Transmitter Target Pressure (kPa) 0.0 20.0 40.0 60.0 80.0 100.0

MSU Applied Value (kPa) Increase Decreas e 0.0 0.0 20.10 20.10 40.10 40.10 60.10 60.10 80.10 80.10 100.10 100.10

UUT Output (mA) Increas e 4.03 5.64 7.24 8.84 10.44 12.04

Decreas e 4.04 5.64 7.24 8.85 10.45 12.05 13

120.0 140.0 160.0 180.0 200.0

120.10 140.10 160.10 180.10 200.10

120.10 140.10 160.10 180.00 200.10

13.65 15.25 16.85 18.45 20.05

13.65 15.25 16.85 18.45 20.05

Table 3: Five Points Calibration of EJA430A Pressure Transmitter No % 0 25 50 75 100

MSU Applied (kPa) 0.0 50.0 100.0 150.0 200.0

Desired output of UUT (mA) 4.00 8.00 12.00 16.00 20.00

Actual UUT Output (mA)

Output Error %

4.03 8.03 12.04 16.04 20.05

0.750 0.375 0.333 0.25 0.25

14