How to Calibrate GRAVIMETRIC COAL FEEDER, BHEL
Hello guys today we are going to learn how to calibration of Gravimetric Coal Feeder supply by BHEL. Gravimetric feeder is that we measure the rate of a gravimetric feeder in the unit of volume per unit time
PURPOSE: This Procedure is intended to provide guidance and instructions for carrying out the Calibration and maintenance of Coal feeder as per standard practices prescribed by OEM or General Industry best practices in safe manner while ensuring minimization of environmental impacts to the extent possible.
DETAILS OF HAZARD INVOLVED:Electric Shocks, Exposure to Dust, Exposure to Heat
Exposure to High Pressure Fluid, Rotating Part & Work at height
SAFETY PRECAUTION REQUIRED:
Use hand gloves while working with the system.
Ensure proper illumination. Use dust mask & safety goggles.
FREQUENCY OF MAINTENANCE:
Annually/When ever required. Standard suggestions of vendors is 6 months for your convenience.
ISOLATION PROCEDURE:
You must get PTW (Permit To Work) Before working switch off the power supply from respective GFCC PANEL form Control Panel Room.
Ensure Isolation of Bunker O/L Gate or feeder I/L Gate & switch off the Power supply.
Ensure respective mills are in OFF condition. Ensure feeder Outlet Gate should be in closed
Ensure the isolator is off. Check the healthiness of main motor by measuring Resistance between R-Y, Y-B, B-R. It should be around 2-3 ohms. Similarly check for COC motor and resistance should be around 65 Ohms.
Check megger for both motor. If megger value is normal then go for further processor
WORK INSTRUCTION:
1. Daily Check List:
Visually check for Load cell bolt tightness.
Visually check any damage of signal cable of Tachometer generator and Load cell.
Visually check for indication in Display units of no coal flow monitor at coal feeder floor at local LCP (Local Control Panel).
2. Load Cell:
Stop the feeder Main motor. Close the seal air supply.
Close the feeder inlet gate & feeder outlet gate.
Open the side doors, Clean the coal on belt.
Check the Load cell is not in calibration mode. it should be in feed mode.
Check the Level between two rollers of weigh and span through levelling bar.
Check the load cell support bolt tightness.
After load cell checking, close the side door.
Use Digital Multi meter to check excitation voltage + 10 V DC across TBF -2 & TBF -3
Check the resistance across TBF-7 & TBF -8 for load cell 1 and TBF-9 & TBF-10 for load cell 2, it should be 100 Ω.
3. AC Tachometer Generator (24 Pole):
Check the tightness of sensor house (use Allen key 3 mm).
Check healthiness of tachometer generator by measuring resistance among terminal TBR2 - 29, 30 & TBR2 - 31, 32. It should be around 250-300 ohms
4. Main Motor and COC Motor:
If Main Motor megger value not as expected then take action to improve megger value.
5. Acoustic Flow Sensor :
Check the tightness of sensor flange.
Check the AC output voltage 215 V AC.
6. Calibration procedure:
Calibration is accomplished in two separate steps
CAL 1: Elimination of system tare, which includes the weight of the weigh roller, load cell support assembly and the feeder belt.
CAL 2: Calibrates the load cell output with a known weight.
7. Calibration Steps:
Ensure the power supply off on GFCC panel. Verify Feeder selector switch SSF (REMOTE/OFF/LOCAL) switch is in OFF at LCP ( LOCAL CONTROL PANEL).
Close the feeder inlet gate.
Open all side doors of feeder and empty the coal on belt.
Ensure calibration weight is not engaged.
Use levelling bars and shim plate ( approx. 0.5mm) to adjust load cells for proper and equal loading between weigh & span rollers. you may check mA at TB 1,2 & TB 3,4 both should be equal mA.
After adjustment remove levelling bars. Tighten load cell check nut.
Switch on the power supply of GFCC panel.
Run feeder motor and ensure the forward and reverse direction.
Ensure and adjust the belt for proper tension and tracking all Roller ( Mainly Weigh and both Span roller ).
Run the feeder and check that the Coal Motion Monitor Relay (CMMR) contact is operated now.
Put four reflective clips on the belt teeth in equal distance (count all the teeth then division by 4).
Put both the calibration probe (CAL1 & CAL2) sensor, adjacent to the weigh span roller and connect the probe cables on the respective receptacles on the LCP. (While fixing the CAL probe, the power supply of GFCC panel should be OFF).
Compare the calibration weight against the value that is stored in the Microprocessor Memory.
To decide the calibration Speed value and enter the value on MPC.
Ensure calibration weight is disengaged from both load cells.
MUST FOCUS ON :
Select ‘CAL’ from LCP selector switch and turn ON the toggle switch in the SCM module in LCP.
After that press ‘TARE’ key from GFCC keypad. This will start the tare calibration.
Ensure the calibration probe sense the reflective clip by observing channel no. 31 & 32 on DIM module in the GFCC panel. Whenever the reflective clip passes the calibration probe-A channel 31 blink and when probe –B channel 32 blink.
The following condition will cause Feeder trip automatically during calibration.
1. Feeder trip during CAL1.
2. Calibration probe not available.
3. Calibration tapes too close.
4. Weighing system volumetric during CAL1.
After 8 Cycle Rotation calibration complete and the display shows the percentage.
a. Repeatability error.
b. If this error is greater than a programmed limit, the display shows:
|
< CAL1 >
Dev: 0.70% Bad! < ENTER >
to reCAL < EXIT > to QUIT |
Press ENTER to make another attempt.
|
< CAL1 >
Dev: 0.20% Good! < ENTER >
to QUIT |
Good Values = 8 |
f. Ensure that COC motor will run when respective feeder runs in forward direction. After successful calibration, remove the T&P from the area, clean the area & return the PTW
g. If Span calibration is successful then calibration process completes. Remove the calibration probe. Turn OFF the toggle switch. Put the LCP selector switch in OFF position. Close the feeder Door. Disengaged the test load. Close LCP door
CHECKS BEFORE RELEASE OF PERMIT
a. All T & P’s and manpower are removed.
b. Clean the maintenance area properly.
c. Normalize all isolation & Return PTW
HANDLING OF CONCESSIONS OR DEVIATIONS:
a. In the Event of Any Changes or Deviation from Procedure are required due to Urgent business requirements or system/Equipment approval should be obtained from Head O&M.
b. The report for the concerned task should clearly Captured the details of deviations and reason for the same.
REFERENCES: OEM Manual
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