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Product Bulletin Release No.1 Oct 2002
EHMU“ELECTRONIC HOIST MONITORING UNIT”
SATISFYING THE REQUIREMENTS CHAPTER 16 OF THE MINES AND WORKS ACT OF THE SOUTH AFRICAN DEPARTMENT OF MINERAL AND ENERGY AFFAIRS
1. PurposeThe purpose of the ELECTRONIC HOIST MONITORING UNIT (EHMU) system is to protect mine winders against over-speed and over-travel events.
2. Overview
The EHMU is a dedicated digital, solid state device, designed specifically for protecting mine winders against over-speed and over-travel events, and complies fully with the requirements of Chapter 16 of the Act of the Department of Mineral and Energy Affairs. i.e. :
“16.8 Last three turns audible warning.16.9.1 Every drum of a winder shall be equipped with –
a) At least one effective automatic upper limit and lower limit over-wind prevention device.
b) An effective automatic over-speed prevention device which shall automatically cause the winder drum to be stopped if the permitted speed is exceeded by more than 15%, or if any conveyance approaches the extremities of the wind at such a speed that an approved degree of protection cannot be maintained.”
The EHMU is a dedicated device, locally designed and manufactured as a direct alternative to mechanical devices currently used for the protection of mine winders, offering superior integrated user friendly features for routine safety auditing, having comprehensive self monitoring and cross checking functions, with an event logging system to assist the Mine Management in analysing the winder performance.
N.B. The philosophy of Winder Controls is that protection and control of a winder should not be combined so as to eliminate the risk of common mode failure.
3. EHMU Principles of Operation
Certain design features are specifically arranged so as to assist the responsible engineer in his task of ensuring the continued safety of the winder.
The password access protection to the supervisor limits, and the structure of the parameter blocks, are but two examples of this approach.The EHMU uses drum position to establish the position and velocity of the conveyance in the shaft. A conveyance position counter contains a real time value that is used to establish the necessary protection profile in terms of the maximum speed allowed at any point in the shaft, as well as absolute travel limits.
4. EHMU Safety
The EHMU is a dedicated stand-alone unit specifically designed and intended for winder protection. The philosophy of Winder Controls is that protection and control of a winder should not be combined so as to eliminate the risk of common mode failure
Dedicated engineering and design assure safety.
Some of the design features of the EHMU are :
1) Dual line execution of all protection functions from the mechanical drive to the encodes to the contacts of the output relays.
2) Program execution run monitor on all cards.
3) Cross check monitoring on each execution line of the following :
a) position counter value
b) speed value
c) monitor card inputs
d) monitor card outputs
e) parameter block data
4) Dual “watch dog” timer relays on the system card, and a “watch dog” timer relay on each monitor card, to ensure that the firmware is being executed within the prescribed period.
5) The system card polls the monitor cards every 10ms and must receive the correct responses.
6) “Fail to safe” relay outputs for all protection functions (i.e. relays de-energise to trip). The drive monitor function employs watch dog relays that monitor a pulse train and thereby checks for an output that is stuck high or low.
7) Output relay contact test (on demand) that sets all relays to the trip state and monitors that the auxiliary contacts are also in the tripped state.
8) There is a datum switch “window” monitor that allows the datum switch to update the conveyance position counter only within the pre-set window. If the switch signal is input at any other conveyance position the counter will not be updated and the internal monitoring will cause a trip. Also if the conveyance counter value passes through the window without receiving an input the internal monitoring will cause a trip.
9) In addition to the pre-requisite shaft mounted datum switch, a second datum switch is fitted to check the position counter value prior to the start of retardation.
10) A third, independent speed/distance protection routine is executed on the system card, and this will provide an overall back-up safety envelope with a separate means of tripping the winder safety circuit.
11) The firmware has been fully tested; developed using state of the art tools and languages; and reviewed by an independent, recognised, expert in the field of micro-controller applications. Since the original development in the Intel assembler most of the firmware has been re-written using a “C” compiler. As well as using standard function modules (which have already been fully de-bugged), the re-write has further improved the quality of the firmware.
12) In addition to providing hardware that is assured “safe”, a prime objective is to ensure that the device will not allow parameter values to be set so as to render the protection functions inadequate, and that the device will monitor possible incorrect use. For this to be successful the setting of the supervisor parameters is of paramount importance.
13) Internal monitoring ensures that comprehensive self checking of all the system components is effected, and that a malfunction will de-energise the output relays to trip the winder.5. EHMU Winder Protection Functions
1) OVER-SPEED TRIP (monitor cards) :
(Dual line) for mid-shaft, retardation, creep and clutching speeds, also for the emergency brake release function if employed.
OVER-SPEED TRIP (system card ) :
(Single line) that compares actual to allowed speed, and provides a separate means of tripping the winder via the watch dog outputs.2) OVER-WIND TRIP :
(Dual line) for top of shaft travel limit.3) UNDER-WIND TRIP :
(Dual line) for bottom of shaft travel limit.4) DRIVE MONITOR TRIP :
(Dual line) for cross check to another independent drive from the winder.5) WATCH DOG TRIP :
(Dual line) for internal monitoring.
6) OVER-SPEED ALARM :
(Dual line) for mid-shaft, retardation, creep and clutching speeds, also for the emergency brake release function if employed.7) MEN/ROCK SELECTED :
(Single line) for status and signal interlocks.8) LAST THREE TURNS :
(Single line) for warning purposes.9) Retard alarm for start of retard warning. This feature is useful for manual, open loop winders.
10) The response time for all protection features is less than 30mS from the event to the opening of the output relay contacts.
6. EHMU Operational Features
1) PROFILE CAPTURE :
The storing of the winder cyclic retardation characteristics, to which is then added the alarm and trip margins for the speed/distance protection envelope.2) STAND ALONE OPERATION :
The philosophy of Winder Controls is that protection and control of a winder should not be combined so as to eliminate the risk of common mode failure
The EHMU is self contained, requiring only a power supply, mechanical drive to the encoders and an external motion detector, to enable it to perform all of its functions.3) STATUS INDICATION :
Modes of operation and input status are readily visible via indications on the front panel.4) EVENT LOG :
The battery backed RAM contains a 1024 event rolling memory of all protective function events as well as certain statuses.5) CLUTCHING OVER-SPEED :
Separately set parameters of mid-shaft speed, operative when either clutch is withdrawn.6) BRAKE TEST :
The battery backed RAM contains a section for storing the actual speed/distance data on every safety circuit trip.
7) FALSE BANK TEST :
The top retardation profile is shifted into the shaft by the value entered to enable run-in tests to be performed.8) VIEW STOPPING DISTANCES :
This may be viewed on the display after every protection function trip.9) PROFILE DISPLAY (or speed difference display) :
LED display indicating the speed difference between the actual speed and the cyclic characteristic. (Similar to over-speed alarm contact gap monitoring on a Lilly controller).10) THREE (3) LEVEL PARAMETER LIMITS :
First (user) level for the maintenance electrician.
Second (supervisor) level for the responsible engineer accessed via key-switch/password.
Third (programmer) level determined by firmware limits.11) KEYBOARD PARAMETER ACCESS :
All user and supervisor parameters are accessed via the integrated keyboard and display.12) PARAMETERS :
All parameters are in SI units.13) ROPE SPEED :
Up to 25m/sec. (This can be increased if required.)14) SHAFT DEPTH :
Up to 3000m. (This can be increased if required.)15) FAULT ANNUNCIATION :
The integrated display annunciates the first protective trip that operates.16) PRINTED OUTPUTS :
The contents of the RAM can be printed on an external printer, via the built in serial port, on demand from the keyboard. The following can be printed :
Supervisor parameter block.
User parameter block.
Brake stopping performance.17) PC COMMUNICATION :
A PC can communicate with the EHMU using the “EHMUDESK” software via the serial port.The following features are available :
Load parameters from PC.
Save parameters to disk.
On line status screen.
Parameter listing and editing.
File management.18) RELAY LOGIC INTERFACE :
To enable direct interchangeability with existing mechanical controllers, a hardwired relay logic interface handles all winder interconnections.19) MID-SHAFT SLOWDOWN :
For special applications, e.g. multilevel, the retardation protection characteristics can be positioned at points in the shaft. Provision is made for a total of eight (8) intermediate levels.20) REDUCED COMMISSIONING TIME :
Many of the features itemised above allow the device to be commissioned in a fraction of the time taken to commission an equivalent mechanical device. On completion a hard copy and disk file copy of the as-commissioned parameters are available for future reference and for loading into replacement cards.21) ALTERNATIVE BRAKE RELEASE PROTECTION :
In the event of a power failure the EHMU is powered from its own built-in battery. A separate settable over-speed trip will be operative as well as the other normal protection functions. The safety circuit for the alternate brake release operation will comprise of the following :
Men selected.
Over-speed trip at 2,5m/s. (adjustable) .
Men over-wind trip (normal setting).
Men under-wind trip (normal setting).
These contacts are wired to terminals as a separate circuit and an input contact to the EHMU sets the alternate brake release mode of operation.7. EHMU Operational Process
Four (4) printed circuit boards perform the processing functions. The hardware for the dual line protection functions comprise an encoder, a monitor card, and output relays. The system card is connected to both monitor cards via a serial link (the micro-controller bus-wires do not leave the individual cards); this link is used to transfer parameters and other data for continuous cross checking between the two monitor cards.
The keyboard and display are also driven from the system card. The balance of the hardware comprises of an un-interuptable battery backed power supply with interlocked time-out features, the input interface relays, and the watchdog timer monitor relays.
The encoders are selected to provide the required number of pulses per revolution by considering the drum diameter and auxiliary drive gear ratio. The design value is between 30 and 99 pulses per 1 meter of rope travel. Direction is determined by the sequence of index and quadrature pulse trains and a system function is provided to select the conveyance direction to suit.
The dual line output relays have their contacts wired in series (“anded”) into the winder safety circuit such that either monitor card can effect an immediate independent safety circuit trip. The system card trips the safety circuit via the watch dog outputs.
Each micro-controller card is equipped with its own voltage regulator, 87C32 micro with internal EPROM, Dallas Smart-watch real time clock and 32k byte battery backed RAM and necessary I/O interface components.
The battery backed power supply has an interlocked power down timer to ensure that the conveyance position is processed and stored in the event of a mains supply failure, and will thereafter disconnect the battery. The EHMU will automatically start up when power is restored. A manual override can be used to run the EHMU from the battery for power supply failure events.
8. EHMU Parameter blocks
These comprise the application parameters as required for a particular winder and are stored in RAM. The EHMU compares the contents of the parameter blocks on a regular basis and if a difference is detected an immediate trip results.
There are separate supervisor and user blocks with the necessary value limiting features.
The parameters can be viewed and changed from the keyboard. They can also be printed on hardcopy on demand.Data can be moved between blocks, and to and from a PC via the built in serial port.
9. EHMU Retardation Monitoring Modes
1) RETARD RATE MODE :
When this mode is selected the EHMU calculates the control profile speed for the current position using the parameters entered.2) PROFILE MODE :
When this mode is selected the EHMU uses the previously captured actual control profile and uses this as the basis for the over-speed monitoring. The profile is determined by the parameters of “profile length” at the high speed end, and “creep distance” at the low speed end.For the profile capture the winder control system must first be set up correctly for its designed position/speed characteristics.
The green LED’s on the monitor cards will flash as the profile is being captured and the winder will be protected in the “Retard rate” mode during this period. On stopping, the profile capture will cease, and will then be transferred to the other monitor card.
10. EHMU Winder Performance Tests
1) FALSE BANK TESTING :
To enable safe testing of the protection system the EHMU can move the end of wind profile into the shaft by a selected distance. This will then cause the winder to trip as the control profile exceeds the protection profile, and the stopping performance can be monitored. Differing values of false bank displacement will cause trips at differing speeds thus allowing a range of results to be obtained.These results can be manually recorded from the display or a brake test print out can be made after each trip test.
2) TURN BY TURN TRIP SPEED TESTING :
This test mode provides the user with means to limit the profile from the stopping position to the turn count selected, and then record the tripping speed at each turn selection.3) BRAKE TESTING :
The selection of “BRAKE TEST” will cause the EHMU to trip on under-wind (for a descending conveyance) and over-wind (for an ascending conveyance) at the entered brake test point. Hereafter a brake test print out can be made, which shows distance and speed characteristics from the point of trip.11. EHMU Verification of Protection Functions
In order to assure that the EHMU is providing the protection required, the following regular checks are to be made to verify the protection functions :
1) DAILY TRIPS :
a) Run the conveyance into the over-wind (or under-wind).
b) Read the trip point on the display.
c) Push the “RESET” and read the stopping point on the display.
d) Confirm the parameter value.2) WEEKLY CHECKS :
a) Confirm adherence to the control profile by observing the monitor cards speed difference display.
b) Confirm over-speed trip at creep speed.
c) Confirm the displayed conveyance position to known depth indication marks.3) MONTHLY CHECKS :
a) Print the parameter block and confirm that the data is within the allowable margin of the as commissioned values.
b) Confirm adherence to the control profile by observing the monitor cards speed difference display.
c) Confirm the over-speed trip at creep speed.
d) Execute turn by turn trip testing.
e) Confirm clutching over-speed.
f) Execute a brake test and print out the results.
g) Confirm last three turns warning.
h) Check the mechanical drive and drive monitor.4) SIX MONTHLY CHECKS :
END OF WIND APPROACH :
a) Run to mid-shaft.
b) Select false bank (with adequate displacement).
c) Run in at selected speeds and record trip point for each speed. If required the over-speed contacts may be bridged to prevent brake distress, and if so, push “RESET” after each trip to clear the display.BACK ENDS (OR ROPE CHANGE) :
a) Do NOT disconnect the drive to the EHMU.
b) For doubling down or rope removal, set the bottom man-landing and the under-wind to allow the rope to be unwound.
c) Set the “RATED ROPE SPEED” to the required value for the doubling down control speed.
d) After completion, and re-attaching the conveyance, take the conveyance past the DATUM switch to re-synchronise the position counter.
e) Revert to normal parameters.
f) Confirm daily trips.
g) Run through the shaft and confirm adherence to the control profile.12. EHMU Hardware Specification
An EHMU consists of a number of items depending on the configuration selected, and will typically consist of the following :
a) Encoders which are base mounted with suitable mechanical drive details.
b) The whole unit is housed in a sheet steel enclosure fitted with suitable furniture.
c) Auxiliary drive monitoring detail.13. EHMU Encoder Assembly
The EHMU encoder will be mounted on a fabricated base assembly including the input shaft coupling, drive to each encoder and couplings. The arrangement will have a removable cover and include provision for the wiring details. The drum size, and the auxiliary drive ratio will determine the selection of the encoder output.
14. EHMU PANEL ASSEMBLY
The EHMU will be housed in a painted, sheet steel, floor mounting, dust excluding enclosure with lockable hinged doors. Cabling will be bottom entry unless otherwise specified, a suitable gland plate and terminals will be provided. The interfacing terminals will be organised to suit the application and adequate disconnecting/testing facilities will be provided.
The electronic modules will be rack mounted, this rack will be mounted in an environmentally protected swing out enclosure that will include the “rfi” and “emi” filters. The keyboard will be a membrane type unless otherwise specified. The display unit will be visible through a glass window.
The input interface will be isolated by means of galvanically isolated opto-couplers within the interfacing PLC, and will be arranged to operate from internal or external power supplies.
The output interface will consist of robust, high integrity relays. These relays will be mounted so as to facilitate fault finding and maintenance.
All components will be readily accessible and labelled as referenced on the schematic drawings for the EHMU. To prevent ambiguity, for a winder with a single EHMU all wire numbers will be pre-fixed with the letter “E”, for a winder with two EHMU’s the left hand drum EHMU will have numbers pre-fixed with the letter “L” and the right hand EHMU with the letter “R”.
The power supply components will be chassis mounted and will include the necessary circuit breakers, transformers, rectifiers, regulators, etc. The battery back up will be of a maintenance free sealed lead acid type. The battery charger will be monitored and have a power failure time out circuit which will disconnect the load from the battery after the winder has stopped. This circuit will have a manual override to allow the protection of the winder for alternative brake control procedures, in this mode the mid-shaft tripping speed will be reduced to the required value for the specific application.
The EHMU will be accompanied by a full set of operation and maintenance documentation including commissioning instructions.
15. General
The existing electrical schematics will be marked up showing all the inclusions and interfacing points. An EHMU as commissioned schematic will be provided.
All site installation will be carried out with minimum interference with the winder normal operation. Final commissioning and putting into service will be carried out over a shut down weekend following a period of approximately three weeks of off line installation and preliminary commissioning.
