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COUPLED TANKS RIG LABORATORY USER GUIDE

VERSION 1.3

Labshare © 2011

Coupled Tanks User Guide Version 1.3

Labshare © 2011 Page 1

Table of Contents 1 Introduction .................................................................................................................................................. 2

1.1 Remote Laboratories ......................................................................................................................... 2 1.2 Couple Tanks - The Rig Apparatus .................................................................................................... 2

2 Rig Session ................................................................................................................................................. 4

2.1 Using the Rig Page ............................................................................................................................ 5 2.2 Data Acquisition ................................................................................................................................. 7

3 Rig Control Software ................................................................................................................................... 9

3.1 Open Loop ......................................................................................................................................... 9 3.2 Closed Loop PID Control ................................................................................................................. 12 3.3 Experiment Data File Transfer ......................................................................................................... 14

4 FAQ & Troubleshooting ............................................................................................................................. 16

0.1 05/2006 First draft Dr. Dikai Liu 0.2 06/09/2010 Revision LaReine Yeoh 1.0 14/09/2010 Internal release Ellie Burke 1.1 15/11/2010 Revision and general formatting Ellie Burke 1.2 03/05/2011 Screenshot updated Ellie Burke 1.3 06/06/2011 Labshare log update Ellie Burke



1 Introduction

1.1 Remote Laboratories Remote laboratories enable students to access physical laboratory apparatus through the internet, providing a supplement to their studies and existing hands-on experience. Students carry out experiments using real equipment, but with much greater flexibility since access can occur from anywhere and at any time. Their interaction with the remote equipment is assisted by the use of data acquisition instrumentation and cameras, providing direct feedback to students for better engagement. Traditional engineering laboratories require students to be physically present in order to work with equipment, which may limit student flexibility. Conversely, remote laboratories let students work in their own time and even repeat experiments for better learning outcomes. Of course students cannot actually touch and feel the equipment in a remote laboratory, but they can still perform most other tasks relevant to their learning. Sometimes, separation from potentially hazardous equipment is preferable from a safety point of view. Due to the increased use of remote operation in industry, where machinery and entire plants are often controlled from a distant location, students may directly benefit from learning how to remotely control equipment. Furthermore, remote laboratories provide the opportunity to access a wider range of experiments as costly or highly specialised equipment may not be locally available. This presents the opportunity to share laboratory facilities between institutions. Significant research and pilot studies have been undertaken in Australia and by several groups around the world into the educational effectiveness of using remote laboratories. These studies have consistently shown that, if used appropriately in a way that is cognizant of the intended educational outcomes of the laboratory experience, remote laboratories can provide significant benefits. Indeed, multiple research studies have demonstrated that whilst there are some learning outcomes that are achieved more effectively through hands-on experimentation (e.g. identification of assumptions, specific haptic skills), there are other learning outcomes that are achieved more effectively through remotely accessed laboratories (e.g. processing of data, understanding of concepts).

1.2 Couple Tanks - The Rig Apparatus The Coupled Tanks Rig was purchased as an off-shelf product, which allows students to study and design a simple control system. Such an apparatus aims to help students develop and verify their mathematical models of the system against the real-world data coming from the Rig. The Coupled Tanks Rig allows students to:

Characterize the behavior of the system

Acquire the appropriate data from which a simplified model of the coupled tanks can be created

Develop PID controllers to control the influx of water, such that the water level in the tanks are kept

constant

Test the controller design on the rig itself

The Coupled Tanks Rig consists of two tanks shown in Fig.1. These tanks are connected together via a small opening at the bottom of the tanks, controlled by a baffle plate. Water is pumped up from a reservoir underneath the tanks via a tube into the top of Tank 1, and then through to the second tank via the baffle connection. The water then flows out of Tank 2 via a small outlet tube (with a valve) and back into the reservoir below.



Figure 1: Coupled Tanks Rig filled to the top.

This setup creates a second order system which can be controlled using a PID or other types of controllers. The flow rate into Tank 1 is provided by a pump, the rate of which is controlled by supplying a voltage (between 0-5V) via the data acquisition unit. The water level in each tank is measured with two capacitive level transducers which provide the feedback for the control system. Their voltage outputs (0-5V) have been calibrated to match that of the water levels in the two tanks. Although 2 level sensors are available, only Tank 2 is used for feedback control as the water is less turbulent and hence the data collected less noisy. Data acquisition and control is implemented using a LabJack UE9 device and is linked to the Rig Server PC via an Ethernet connection. The control software from which users drive the Rig is written in LabVIEW and is hosted on a remote machine running Windows XP. Two control software applications are available, one for Open Loop and a second one for PID. There are 2 main processes involved – acquisition and control (if in closed-loop mode). The LabJack is set to acquire the water level in the tanks at 400Hz. Data is extracted from this stream every half a second from which the 200 datapoints collected are averaged to reduce the amount of noise in the water level transducers. This output is then fed into the PID controller which also executes every half a second to match the acquisition rate. Two iSight webcams are connected to the network, which provide visual feedback of the rig in action, with a small time delay.

iSight webcams

Reservoir with submerged

pumps Outlet valve

Water level transducers

Inflow tube

Water level indicator

Baffle plate controlling flow between tanks



2 Rig Session

The following section outlines the procedure for utilizing the Coupled Tanks Rig, which is similar to other Remote Laboratory Rig types used in the past. The software that runs the Remote Laboratories and provides access to the rigs through a web browser is called Sahara. For the purpose of using the rig, it is assumed that users have access to a workstation that meets the system requirements. Users should refer to Labshare’s Generic Rig Access Guide for this information. After logging in with a username and password, the user will be directed to the “Rig Selection” page. Selecting the generic “Coupled Tanks” rig under Rig Types will randomly allocate the user to an available rig. However, if the user wishes to access a particular rig, then one of the rig numbers under Specific Rigs can be selected. Once the rig is selected, a popup will appear, asking if the user wishes to join in the queue for the chosen rig. By clicking “Queue” button, the user now has an access to the selected Coupled Tanks rig. A confirmation request from the current browser may pop up before proceeding with the rig session.



2.1 Using the Rig Page

If the rig is free, the user will immediately be taken to the rig page where the user can access the Couple Tanks rig control software. Each user has a designated session timeframe to conduct a desired number of experiments. A countdown timer at the top left of the page shows how much time the user has left on the rig. This may be automatically extended if no one else is waiting for the rig. The rig session starts as soon as the user is directed to the “Rig Session” page. If the user does not utilize the rig session within the timeline that is given, the rig session may be forfeited.

The rig session starts as the user clicks on the green “Launch” button at the bottom left of the screen. A confirmation request from the current browser may prompt. This will open up a new window in which the LabVIEW control application will be automatically launched from its remote location. Note that it may take a couple of seconds for the user’s remote connection to be established. Next screenshot indicates the user interface that is properly launched to use.



Once finished with the experiment, the user can exit by closing the control software window or pressing the red “Terminate” button under Rig Control at the bottom left of the Coupled Tanks Session page. This will allow the rig to shut itself down and close the control software properly. If the user has finished using the rig completely, back in the Coupled Tanks Session page, then the user can exit the session by pressing the “Finish Session” button. A popup will appear asking for confirmation of exit. Selecting “Yes” will close the current remote connection to the rig and bring the user back to the Rig Selection page. It is important that the user exits the current rig session properly before logging out of the Remote Labs web page to allow other users to access the rig. Once successfully logged out, the user will be redirected to the main login page of Remote Labs.



2.2 Data Acquisition

If data has been saved during any of the rig experiment runs (and not deleted during session), these files can be accessed and collected by the user during the rig session. Or the user can collect saved data files from the “Data Files” link (circled in red) on the Rig Selection page.



This page consists of a collection of all the data files a user has collected from the rigs, listed in chronological order. Selecting one of the files will prompt the user to download the data to the current local drive.

Currently, the Remote Labs server has a limited space; therefore, all data files on the server should be deleted when it is no longer needed. To exit the Remote Labs page itself, the user can click on the “Logout” button at the top right of the screen. Once again, a popup will appear asking for confirmation. Once successfully logged out, the user will be taken back to the main login page of the Remote Labs.



3 Rig Control Software

This section describes how to use the Coupled Tanks rig control software created in LabVIEW. Once the connection to the remote environment is established, the control software is automatically launched within the Java Remote Desktop session. Upon launching the rig control software, the user will be presented with 2 software control options, Open Loop or Closed Loop PID Control. The user can click the one to use, which will open the corresponding application.

3.1 Open Loop The Open Loop application will automatically run through its initialization routine upon launch, which involves checking to see that the water levels are at the right starting position. Once this is completed, the white status bar under the rig model will read “Rig is ready for experiment”, as shown below.



A visual model of the coupled tanks is displayed on the left portion of the control application. A red pump control shows that no voltage and hence zero flow rate, is being applied to the pump. Each tank has an indicator which is calibrated to display the tank’s current water level in millimeters. The water levels of the visual model in both tanks and the reservoir will rise and fall to match those of the actual rigs in the video feed, depending on how much pump action is taking place. The graph on the right is constantly updated to show a plot of both the current water level in Tank 2 (blue) and the flow rate (white) in real time. To start a pump, enter a non-zero flow rate number (in L/min) into the pump control icon. The pump of the visual model will turn green and water should start flowing from the reservoir into tank 1, both indicated on video screens and the visual model. The chosen flow rate will show up on the vertical axis scale on the right side of the graph. As the tanks fill up, Tank 2 Level trace in the graph will increase accordingly.

A “Start Save” and “Stop Save” button are located below the graph, so that the user can manually start and stop saving the data at any time during a run. By clicking on the “Start Save” button, an ASCII file will be created where data is automatically recorded – as indicated in the status bar. The saved Open Loop data consists of 3 columns:

<Time (s)> <Tank 2 Level (mm)> <Pump Flow Rate (L/min)>



After the data has been collected (eg. When steady state is reached), “Stop Save” button should be selected to quit recording the data. The status bar will indicate “Streaming Off”.

To empty out the tanks, enter zero for a flow rate into the pump control icon – the icon will turn red, and the pump action will stop so that the water will slowly drain from the tanks.



Once the tanks are empty, the rig is ready for the next experiment run.

3.2 Closed Loop PID Control The Closed Loop PID control application works in a similar fashion to the Open Loop application. Upon startup, it will automatically run through its initialization routine upon launch. Once this is completed, the white status bar below the visual model will read “Rig is ready for experiment”. Note: the user does not need to leave the Coupled Tanks rig page to switch between using the Open Loop and Closed Loop control software – just close the Java remote session by clicking on the red “Terminate” button and then clicking on the green “Launch” button to re-establish the remote session with the control software application.



The Setpoint and PID gain parameters are located above the visual model. The Setpoint can also be adjusted using the yellow, vertical sliding bar on the Tank 2 visual model (circled in red). The graph on the right displays the:

Setpoint (yellow) Process Variable - Tank 2 water level (blue) Control Effort - Pump flow rate (white)

As the PID parameters change, the amount of control effort applied by the pump will also vary. An example of the rig’s response to some PID gains is given below, with steady state being reached after a short period of time.



Saving data and file retrieval works the same way as the Open Loop control application. However the control data files consist of the following columns: <Time(s)> <Kp> <Ki> <Kd> <Setpoint(mm)> <Tank 2 Level(mm)> <PID Output(L/min)>

3.3 Experiment Data File Transfer All data saved during an experiment run are automatically copied to a server where it can be accessed via the rig page under “Session Files”.



Any additional files for subsequent runs are stored here consecutively. To save a copy to the current local drive, the user can simply click on the file – a popup will then appear asking the user for the details of where to save the file. For user convenience, all files are named with the following convention:

<YYYMMDD>_<Timestamp>.txt Once finished using the rig and collected all the data needed, the user can exit the Coupled Tanks control software by clicking on the red “Terminate” button under Rig Control on the web page. The button will change to yellow as the rig initiates its shutdown procedure including the automatic exit of the control software.



4 FAQ & Troubleshooting Any questions regarding the nature of assessment tasks should initially be directed to the relevant academic. If the user encounters any difficulties using the rigs, the “Contact Support” button should be used to request assistance and report an incident. The following popup window will appear, allowing the user to enter name and a valid email address. Then the most appropriate category should be selected from the drop down list, and the purpose of the help request should be briefly stated. A more detailed description of the problem, comment or request can be given in the feedback box.

Users are strongly encouraged to leave feedback and comments of their experience with the rigs to help improve the system, as well as any suggestions for additional features to be included in the future. For any enquires or assistance, contact the Labshare helpdesk at:

[email protected]

mailto:[email protected]�

tanks rig laboratory ser guide - labshare - home€¦ · coupled tanks user guide ... if data has...

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