17
Calibration
Alternative method for checking output
If you do not have an Anderson-Negele Test Meter, use a Dig-
ital Multimeter (DMM) and the Load Stand
®
II junction box to
monitor the voltage output of each Load Stand
®
before and
during installation. Set up the DMM as described below.
1. Disconnect the white wires from the W terminals on TB1
and TB2 in the junction box, see Figure below.
2. Connect the DMM (+) probe to the W terminal on either
TB1 or TB2
(See A).
3. Connect the DMM (-) probe to TP1 in the junction box
(See B).
Using DMM and Junction Box to Monitor Voltage Output
4. Set a voltage range on the DMM that will accommodate
a measured range of ±1 volt.
5. See Pre-Check Procedures, for details on checking the
voltage output before installation. See Leveling Vessel,
Hardware Installation, for details on monitoring the
voltage output to determine if the vessel weight is
evenly distributed among the Load Stands.
6.
Once output is verified, reconnect the white wires on
the W Terminals on TB1 and TB2 in the junction box.
B W R SHLD B W R
TB1 TB2
B W R B W R B W R B W R
SENSOR A SENSOR B SENSOR C SENSOR D
LOAD STAND STANDARDIZATION
TB
3
TP1
TP2
TP3
(B) Connect DMM
(-) probe to TP1
12 VDC Excitation Voltage from
Signal Processor connected on
Black and Red Terminals
A) Connect DMM
(+) probe to either
W Terminal (TB1 or TB2)
Cable from Previous
Junction Box (if applicable)
Cable to Next Junction
Box or Signal Processor
Calibration
Calibration methods
Before calibrating, you must install a signal processor.
There are two calibration methods:
· Live Load calibration: set lo span and hi span while mov-
ing material into or out of the vessel. This is the preferred
method.
· Manual calibration: set scale factor counts, scale factor
weight, and zero calibration value without moving materi-
al. This method is less accurate than Live Load calibration.
A Live Load calibration requires you to move a known
quantity of material into or out of the vessel while perform-
ing the procedure. The quantity of material moved must be
at least 25 % of the vessel’s total capacity to provide best
accuracy. Live Load calibration is also based on the material
weight currently in the vessel.
Manual calibration allows you to start using the system as
soon as sensors, junction boxes, and signal processor are
installed and wired, even if you cannot
move any (or enough) material now. Manual calibration
values are based on system parameters, including sensor
sensitivity, vessel stress, and signal processor A/D converter
sensitivity. These values are known, can be calculated, or
can be obtained from the signal processor. Manual calibra-
tion is also based on the material weight currently in the
vessel.
Note that manual calibration does not take into account
the actual response to changes in weight. Theoretically, a
change in weight results in a proportional change in digital
counts. However, the structure.s actual response to load and
interaction with piping, catwalks, a roof, discharge chutes,
etc. prevents the system from achieving theoretical values.
Manual calibration is a good start, but to obtain the highest
accuracy, perform a Live Load calibration when scheduling
permits you to move material into or out of the vessel.
Refer to the signal processor manual for the procedure to
input calibration parameters.
Summary of Contents for Load Stand II
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