STX Signal Transmitter Installation and Operation ... - Kistler-Morse

Appendix C. MVS-STX Calculation of Manual Calibration Parameters
Calculation of the pre-calibration parameters
is also dependent on sensor type.
Procedures are given below for:
• Bolt-on sensors (L-Cells and Microcells)
• Direct Support Sensors (Load Stands,
Load Discs, and Load Links)
Bolt-On Sensors
Note
In this procedure, use the value for
Cnts/mV from the MVS.
Calculate the pre-calibration parameters:
1. From the sensor manual/data sheet,
record the sensor sensitivity (S). The
sensor sensitivity has units of mV/psi or
mV/kg/mm 2 .
2. Refer to the Application Data Form for the
vessel (if you cannot locate the completed
form, contact K-M for a copy).
Record the vessel working capacity and
the corresponding stress.
3. Record the current live load in the vessel
(lbs or kg).
4. Calculate the calibration values:
ScfWgt = working capacity (lbs or kg)
ScfCnt = S x Cnts/mV x
Stress (psi or kg/mm 2 )
Zero_Cal = current live load (lbs or kg)
Note
ScfWgt and ScfCnt are input in the
Manual Menu, while Zero_Cal is input
in the Auto Menu.
Example: You are using L-Cells to monitor a vessel.
The vessel currently has 50,000 lbs of material in it.
You go to the Disply submenu in the Manual calibration
menu and write down the Cnts/mV — 699.05.
Following the pre-calibration procedure:
1. S = 35 mV/1000 psi (from L-Cell manual)
2. From the Application Data Form, the working
capacity is 200,000 lbs and the corresponding
stress is 1892 psi.
3. Current live load = 50,000 lbs
4. Calculate the calibration values:
ScfWgt = working capacity (lbs) = 200,000 lbs
ScfCnt = S x Cnts/mV x Stress (psi)
= 35 mV/1000 psi x 699.05 Cnts/mV
x 1892 psi
= .035 mV/psi x 699.05 Cnts/mV x 1892 psi
= 46,291 Counts
Zero_Cal = current live load (lbs) = 50,000 lbs
Direct Support Sensors
Note
In this procedure, use the value for
Cnts/mV from the MVS.
Calculate the pre-calibration parameters:
1. From the sensor label or manual, record
the Rated Load for one sensor.
2. From the sensor label or manual, record
the sensor sensitivity (S). The sensitivity
has units of mV/V. Calculate and record
the average sensitivity if the system
has multiple sensors with slightly
different sensitivities.
3. Record the excitation voltage for the
system. Typical excitation values:
• K-M silicon sensors — 12 Volts
• Foil gage sensors — 10 Volts
4. Record the current live load in the vessel.
5. Calculate the calibration values:
ScfWgt = Rated Load (lbs or kg) x
Number of Supports
ScfCnt = S (mV/V) x
Excitation Voltage (V) x Cnts/mV
Zero_Cal = current live load (lbs or kg)
Note
ScfWgt and ScfCnt are input in the
Manual Menu, while Zero_Cal is input
in the Auto Menu.
Example: You are using load cells to monitor a vessel
with four legs. The sensors have a sensitivity of
30mV/V and a rated load of 100,000 lbs. The vessel is
empty (contains 0 lbs of material). You go to the
Disply submenu in the Manual calibration menu and
write down the Cnts/mV — 699.05. Following the
pre-calibration procedure:
1. Rated Load for one sensor = 100,000 lbs
2. S = 30 mV/V
3. Excitation Voltage = 12 V
4. Current live load = 0 lbs
5. Calculate the pre-calibration values:
ScfWgt = Rated Load (lbs) x number of supports
= 100,000 lbs x 4 = 400,000 lbs
ScfCnt = S x Excitation Voltage x Counts/mV
= 30 mV/V x 12 V x 699.05 Cnts/mV
= 251,658 Cnts
Zero_Cal = current Live Load = 0 lbs
C-2