Sancar J. Fredsti (Fredsti Industries, 20 Adair Drive Ste:D, Carson City,
Nevada, 89706, USA. jim@fredsti.com)
Jon Fox (Mackay School of Earth Sciences & Engineering, University of
Nevada, Reno, MS 173, Reno, NV 89557, USA. ag.jonfox@ymail.com)
Pierre Mousset-Jones (Mackay School of Earth Sciences & Engineering, University of Nevada, Reno, MS 173, Reno, NV 89557, USA.
mousset@mines.unr.edu)
A Laboratory Mine Ventilation System with VOD for
Teaching Mining Students
Key words: VOD Laboratory Student Teaching Mine Ventilation System Research
Abstract
A model mine ventilation network has been used as a teaching tool for many years
in the Mine Ventilation Laboratory at the Mackay School of Earth Sciences and Engineering (MSESE) in Reno, Nevada. It has gone through three phases of upgrade
and the latest one has just been completed. It consists of a three level mine with
intake and exhaust shafts, adjustable main and booster fans, regulators, multiple
pressure and quantity measuring units, CO2 injection ports and analysers, etc.,
which are all controlled by a modern computer system. The model and equipment
specifications are described in reasonable detail so that others in the mining engineering educational community can build a similar system in their laboratories. It is a
relatively inexpensive teaching tool to build that can be used to demonstrate a wide
variety of mine ventilation principles and a Ventilation-on-Demand (VOD) system,
and it can also be used for research purposes.
Introduction
The first model was designed and built with the help of Dr. Wala from the
University of Kentucky (Wala A. 1984). It was used primarily for teaching
purposes, however, several research projects were carried out using the
model to investigate controlled recirculation systems (Calizaya F. 1988), and
modelling the inflow of methane from the gob areas of a coal mine (Danko
G. 1989). In order to do this research some further modifications were made
to the system, until a major upgrade took place (Mezei C. 2001) with a more
capable computer system.
Recently, it was decided to carry out a further upgrade not only of the computer and related software but the physical system itself using the latest
technology. The intent was to make it a representative demonstration unit of
the principles of VOD to the students. This was recently completed (Fredsti
S. 2012) and the system is currently being tested and refined for use in future mine ventilation classes. In order to help mine ventilation personnel in
the industry, it is possible to make the model accessible via the Internet, and
it is hoped to implement this in the future.
While mine ventilation network simulation is typically covered in a undergraduate mine ventilation course, it is considered important for students to
also have hands on experience in measuring ventilation parameters in a
mine, physically modifying a ventilation system, and comparing the physical
system results with those produced by the simulation. This is often not practical for the students to do at an operating mine, hence, the need for this
model, which is one part of an extensive mine ventilation laboratory at the
MSESE. However, the students do carry out a ventilation survey at an operating underground mine as part of the mine ventilation course requirements.
There are physical models available to demonstrate mine ventilation principles that may be purchased at a considerable cost. The purpose of this paper is to provide educators with sufficient detail so they can build a similar
system in their mine ventilation laboratory for a reasonable cost. A constraint
in many universities is available laboratory space, and the advantage of this
model is that it can be configured to the available space and does not occupy much of that space.
The model mine is constructed from PVC plastic pipe approximately 10 cm
in diameter, though this can vary. Figure 1. shows part of the system at the
MSESE. Since the pipe is usually quite smooth it might be necessary to add
some artificial resistance in the pipe to generate a reasonable pressure drop
in the system. Contained within the model is an array of pressure sensors,
anemometers, regulators, CO2 injection and analysis ports, and fans. These
devices allow the student to change the system’s operating parameters and
observe the results in real time on a personal computer.
Distributed digital processing of the network module’s control and feedback
error-free transmission is via a 4-wire communications bus. This real time
approach for control and feedback is coupled with capture of the feedback
into a database to allow for further analysis. Each network sensor and control element are described in the next sections, followed by a description of
the control network and communication protocol. Finally, the control interface program functionality and layout are discussed.
Figure 1. Views of the model ventilation network in the Laboratory.
1. System Description:
The plastic pipe is configured into the mine network consisting of intake and
exhaust shafts, three levels, and interconnecting raises, and is mounted on a
steel strut channel frame attached to the laboratory wall, see Figure 1. The
joints are sealed using either rubber sleeves or "duct" tape, ensuring sections of the system may be disassembled for modifications. Arranged in the
system are fans, regulators, pressure sensors with pitot tubes, hot wire anemometers, CO2 sensors and CO2 injection points, see the ventilation system control schematic in Figure 2. The system is controlled by a host PC
attached to the communications network and powered by distributed power
supplies.
Network sensors and control points are placed in the air stream by drilling
and tapping the PVC pipe at strategic locations, then installing the various
instrument sensing probes. Pitot tubes and anemometers are placed in the
centre of the air stream while CO2 sensing and injection points are located
along the walls of the pipes. Fans and regulators are attached to the network with reducers, adapters and manifold assemblies, facilitating connection to the PVC piping network.
Figure 2. Ventilation control system schematic and user interface.
The control and feedback instrumentation package system is a network of
modules interconnected by a common communications and power bus. All
communications for the system is via a single RS-485 half duplex serial
communication protocol controlled by the host system, running at a 38,400
baud rate. Each module has internal voltage regulation and filtering and
draws a small amount of power (~30 milliamps), for its internal digital and
analogue circuitry, from the 12-volt DC bus. Each instrument on the bus has
a unique network address and responds to control and query commands
sent across the network in an error detecting packet and uses software
handshaking to verify information transmission and reception.
2. Fans:
The parallel exhaust fans use brushless motors, see Figure 3a. The fans are
mounted using an appropriate manifold onto the PVC pipe. The fans can
operate in single or dual mode and between 1000 and 5000 RPM using a
variable speed controller. The system can create pressure differentials exceeding 1500 Pa.
Booster fans, see Figure 3b, are placed in two locations in the system. One
single booster fan and one with two fans in series, with brushless DC motors, are mounted on the PVC pipe. In the two fans in series can be operated
in single or dual mode.
Figure 3a. Main fans: A) GPIO module B) RPM sensor. Figure 3b. Booster
Fan: Two fans in series
2. Air flow Regulators:
The system has four variable aperture airflow regulators, see Figure 4.
These are constructed from 150 mm optical iris diaphragms, see Figure 5,
and are mounted between PVC adapter plates machined to accept the iris
mounting ring. A screw mechanism is powered by a stepper motor to control
the regulator opening. The iris diaphragms are controlled to vary between a
100% to 5% opening, and have limit switches. The drive module for the
stepper motor recalibrates itself when the system is started or reset. It takes
approximately 100 seconds to move from fully open (100%) to fully closed
(5%). Distributed 24-volt DC power supplies energize the stepper motors.
Figure 4. Iris regulator at 100% open A) 100% open limit switch, B) iris actuator, C) pressure sensor module, D) RS-485 network connection, E) 5%
open limit switch, F) iris adapter plate.
Figure 5. 150 mm optical iris diaphragms, at A) 100%, and B) 5% open.
4. CO2 Injection and Measurement Equipment:
The system has three CO2 injection ports, see Figure 6, to introduce gas
from a compressed and regulated source at 0.2 kg/cm2. This gas is injected
into the system using a pulse width modulated (PWM) valve. The PWM
valve pulse width is determined by a control setting within the host system
and allows for precise gas injection control from 2 to 50 litres per minute.
Control of the PWM valve timing is accomplished with digital General Purpose Input Output (GPIO) modules.
There are five CO2 sensing nodesin the system, see Figure 6. Each node
consists of a 0 to 5000 ppm CO2 sensing module attached to the PVC pipe.
These modules have self-contained pumps, filters and interface electronics.
An analogue GPIO module digitizes the voltage output measurement from
the CO2 sensing modules. While the system is in operation the CO2 levels
are constantly being sampled and reported. It takes less than 2 seconds to
completely exchange the gas within the CO2 sensing module, thus a fresh
air sample is taken for each data query cycle.
Figure 6. CO2 A) injection and B) measurement devices.
5. Velocity and Pressure Sensors:
Velocity determinations are accomplished using four hot wire anemometers,
see Figure 7a, distributed strategically throughout the system. A typical student task will involve anemometer calibration utilizing nearby pitot tube pressure readings. The analogue output from each anemometer is fed to one
analogue GPIO module for conversion and data reporting. Upon module
query, the digitized data is scaled and given offset correction to remove errors then transmitted to the PC host as airflow velocity readings. The analogue GPIO modules contain an internal 16-bit ADC that acquire data every
2 milliseconds, then averaged over 50 samples and the result is reported.
Figure 7a. Velocity Sensor: A) Hot wire anemometer, B) velocity sensor
module. Figure 7b. Pressure Sensor: D) GPIO module, E) pitot tube, F) RS485 network connection.
The system has 20 pressure sensors, see Figure 7b, and each employing
dual differential pressure sensors. These sensors allow for acquisition of
static, velocity and total pressure readings from each pitot tube. Each pressure sensor is sampled 82 times per second and the results are averaged
over 100 samples, which removes the low pressure signal "noise”. The voltage outputs from the sensors are converted by self-zeroing and calibrating a
16-bit analogue to digital converter integral to the module. The output samples are transmitted only when a request is received from the host PC. The
pressure modules must be given 30 seconds to self calibrate, with no fan
operation, during power on or after a system reset.
6. Systems Communication and Network:
All modules and control points are connected via a single 4 conductor
shielded 18-gauge cable. Two conductors carry the 12-volt DC module distributed power and the second two wires carry the RS-485 communication
signal. The cable shield insures signal integrity and is connected to the
common ground power on all modules. At each module the bus is terminated with a 4-conductor 3.5mm keyed plug so that modules may be serviced if
necessary by simply unplugging them.
The communications is based on a half duplex RS-485 serial protocol running at 38,400 baud rate. The protocol uses a packet based variable length
serial stream with embedded formatting, control and data integrity characters. The protocol includes multiple redundant error correction methods,
providing a robust fault detection control and feedback environment.
The user interface program running on the host PC processes all control and
feedback signals. Control and feedback signals are formatted into data requests and responses. The host PC initiates all data requests to the network
modules and only accepts feedback from a module immediately following
direct interrogation by the host. Under no circumstance will a module initiate
traffic on the network.
7. Control Interface Program:
A program written in National Instruments Lab Windows CVI, see Figure 8,
provides point of control and system monitoring during simulation operation.
This program interfaces to the system via a special half duplex communications link and a driver created specifically for this purpose. The program interrogates each system component during a 3 second period. Each module
within the system replies with its gathered data during this period. The data
is then sent to a memory array and to a real time data gathering folder.
During simulation, the main system graphic screen, see Figure 2, is displayed which depicts the overall status of the system operation. From this
screen the major points of operational interest are displayed, such as fan
speed, pressures throughout the system, Iris opening percentage, CO2
measurement, and anemometer readings.
An icon on the desktop represents each system component and in the immediate vicinity of the icon is a text box that displays the latest gathered information for that system component. Clicking a system component icon
displays a graph, see Figure 8, displaying information gathered from the past
hour. When a control component is selected, a text input field relating to the
device’s control range and a corresponding bar graph are displayed. By
changing the input value the device control initiates and the bar graph displays the appropriate feedback.
A small sample of the control system software, authored in C++, see Figure
9. The code sample listed gathers feedback packets from the network CO2
sensors and scales the output for graphic display.
Figure 8. A) Fan speed graphs, B) Fan speed control, C) CO2 sensor
graphs, D) CO2 injector control, E) Iris regulator control, F) Pressure sensor
graph.
Figure 9. Code sample for CO2 sensors.
Conclusion:
A realistic and robust VOD ventilation system model has been described
which can be designed, constructed, and installed in most university mine
ventilation laboratories. A partial parts list is provided in the Appendix and, if
needed, the authors can be contacted for more detail.
References
Calizaya F., McPherson M., Mousset-Jones P., 1988, Controlled Air Flow Recirculation: A Comparative Study of In Line and Cross Cut Recirculation Systems, Proceedings, 6th Annual Workshop, Generic Mineral Technology Center, Mine Design
and Ground Control, University of Alaska, Fairbanks, AK, USA.
Danko G., Rao M., Mousset-Jones P., 1989, Numerical Modeling and Control of Gas
Concentration in Underground Mines, International Journal of Microcomputer Application, Vol. 8, No. 3, pp. 1-12.
Fredsti S., 2012, Selecting and Defining Command and Control Systems for Mine
Ventilation, Proceedings, 14th North American Mine Ventilation Symposium, Salt
Lake City, UT, USA.
Mezei C., Mousset-Jones P., 2001, A Computer Controlled Airflow System for
Teaching the Principles of Mine Ventilation, Proceedings, 3 rd International Mine Ventilation Congress, Krakow, Poland, pp. 605-614.
National Instruments Corporation, 2012, NI LabWindows™/CVI for Windows,
http://sine.ni.com/nips/cds/view/p/lang/en/nid/11107
Telecommunications Industry Association, 2003, Electrical Characteristics of
Generators and Receivers for Use in Balanced Digital Multipoint Systems, TIA/EIA
Standard RS-485.
Wala A., Mousset-Jones P., 1984, Upgrading the Mine Ventilation Laboratories of
the Universities of Kentucky – Lexington and Nevada - Reno, Proceedings, 3rd National Collegiate Association for Mining Education Conference, Lexington, KY, pp.
236-265.
Wala A., Mousset-Jones P., 1984, Physical Model of a Computerized Mine Ventiltion
Network, Proceedings, International Symposium on Underground Mining, University
of Nottingham, England, pp. 1-10.
Appendix:
NI LabWindows™/CVI for Windows Development Suite
(The model C++ source code can be obtained by contacting UNR)
Equipment List:
1) CO2 Sensor (New)
CO2 Sensor Module; Model K-30; www.co2meter.com
2) CO2 Sensor (Old)
Fuji Electric; Model ZFP5; www.fesys.co.jp
3) Anemometers
Kurz; Model 415-3 Hot Wire Anemometer; www.kurz.com
4) Pressure Sensor Differential
Freeescale Semiconductor; MPXV7002; www.freescale.com
5) Pressure Sensor Absolute
Freeescale Semiconductor; MPX5700A; www.freescale.com
6) DewPoint Sensor
General Eastern; Dew-10 ; www.ge-mcs.com
The following are the modules used in the model. The modules or the documentation package which includes information to build the modules and the
associated software can be purchased from Fredsti Industries.
Dual +/- 2 Kilopascal Pressure Sensor Module
General Purpose Digital and Analog Input/Output Module
Dual Fan / Blower Control Module
24 Volt 3 Amp Stepper Motor Control Module
Barometric Pressure and Temperature Module
0-5000 PPM CO2 Gas Analyzer Module
RS232 to RS485 Half Duplex Communications Control Module