Related information:
Summing Junction Box
Introduction
Summing Junction Box
Installation Guide
-Controls
-Mounting
-Wiring
-Leveling
Summing Junction Box
Calibration
Summing Junction Box
Troubleshooting Guide
Summing
Junction Box
Features &
Specifications |
These steps are for Installation Calibration. For
maintenance calibration Go To Maintenance
Calibration.
Summing-J-Box Installation Calibration
NOTE: The Summing Junction Box, as
shipped from the factory, is preset to a null state. If the settings have been
changed the Summing Junction Box must be reset to null before proceeding. To
null: unplug all load cell connectors and turn all switches to 0.
Be sure R-CAL switch is in the weigh position. Turn all SPAN
potentiometers fully counter clockwise. Turn on one load cell switch at a time and adjust
the corresponding ZERO potentiometer for 0.000 mVdc monitored at the
signal test points. Do this for each load cell circuit. Reinstall load cell connectors.
The Summing Junction Box is now in a null state.
Follow the steps listed below for zeroing and trimming all
load cells within the system. If less than four load cells are connected to the Summing
Junction Box, the switches for the unused load cell circuits must be left in the
"0" position.
- Turn all S (span) potentiometers fully counter
clockwise. Be sure all switches are OFF.
- Turn on load cell #1 (S1) and zero displayed weight (millivolt
output) using (zero) potentiometer, turn OFF load cell #1 (S1) and repeat for all other
load cells connected to the Summing Junction Box. This will remove all TARE weight from
the indicator display (digital millivoltmeter).
- Turn all switches with load cells connected ON (they will
remain on during normal operation). Calibrate ZERO for weight indicator following
manufacturer's instructions.
- If "dead load" is supported equally by all load
cells, load the scale to greater than 50% capacity. If "live load" is supported
equally, skip steps 5 through 8 and proceed to step 9.
- Turn OFF S1 through S4, turn ON one cell at a time and record
the measurement device display value. Only one switch at a time must be ON during
this step.
- Trim all higher outputs to match the lowest observed
measurement of step 5 using the (S) span potentiometers. Turn ON one load cell at a
time, adjust the trim, turn OFF the load cell and repeat for all except the lowest reading
load cell connected to the Summing Junction Box.
- Remove the load from the scale.
- Turn ON all used load cell circuits, ZERO indicator as in step
3.
- Apply a known weight amount to the scale equal to or greater
than 50% of scale capacity, calibrate indicator span per manufacturer's instructions.
- Remove calibration weight from scale, set R-Cal switch to test
position, record the mV signal/weight reading as "System shunt number". Turn off
all load cell circuits, turn on one circuit at a time and record that circuit's shunt
number (these shunt numbers are essential for scale calibration verification and
troubleshooting). Set R-Cal switch to "WEIGH" position and turn ON all circuits.
Calibration is complete.
Summing-J-Box Maintenance
Calibration
Periodic calibration checks should be performed to ensure
scale accuracy is within system tolerance.
- With all used load cells ON, empty the scale and verify
indicator ZERO +/- system tolerance.
- With all used load cells ON, empty scale and set R-Cal switch
to "test". Verify the indicator reading matches the recorded 'System shunt
number" of the last scale calibration +/- system tolerance. If an out of
tolerance condition exists, the scale must be recalibrated. This method is as
accurate as using known weight and is much more convenient.
- Scale system tolerance is simply the sum total of uncertainty
of accuracy for each component of the system. This uncertainty varies from component to
component and manufacturer to manufacturer. The National Scale Summing Junction Box has an
extremely low uncertainty after integration and calibration due to the fact it is
comprised of purely passive components. Typically, a system tolerance of +/-0.1% is
readily attainable.
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