Hardy HI 1756-nDF - Manual (Page 48)

44
●
●
●
●
●
Chapter 5
For example, a 2mV/V load cell/point will respond with a maximum of 10 mVDC at the
load sensor’s full weight capacity, which includes the weight of the vessel and the weight
of the product as measured by the load cell/point. Thus, if the load cell/point weight
capacity is rated at 1000 pounds, the load cell/point will be 10 mVDC at 1000 pounds,
7.5 mVDC at 750 pounds, 5 mVDC at 500 pounds and so on.
A zero reference point will
vary from system to system
depending on the “Dead Load”
of the vessel. “Dead Load” is
the weight of the vessel and
appurtenances only, with no
product loaded. In our
example we will assume the
dead load to be 500 pounds.
The operating range for the
scale in this example is 5-10
mVDC with a 500 pound
weight range. Note that after
zeroing the instrument, the 0
reading refers to the zero
reference point and not
absolute 0 mVDC or absolute
0 weight.
Millivolts/Weight Scale
NOTE Load cell/point measurements are checked with a digital volt meter at the J1 connector
on the front of the module or by using INTEGRATED TECHNICIAN with the HI 215IT
Junction Box.
Load Check
Place a load (weight) on the scale or vessel, and check to see if the weight reading on the
input table changes in the proper direction.
For example: If the input table display reads 100 pounds and a 20-pound weight is placed
on the vessel or scale, the ladder logic display should read 120 or some value over 100.
With the input table display reading 100 pounds, if a 20-pound load is placed on the
vessel or scale and the reading is 80 pounds, the reading is going in the wrong direction
and indicates some problem with the system.
If the input table reads improperly or shows no change, something is wrong with the
setup. If the input table changes weight in the proper direction, remove the weight and
proceed to calibrate the module. Refer to chapter 6 troubleshooting for additional help to
determine the cause of the poor weight reading.
AOP Calibration
Both C2 and Hard calibrations are available in the AOP dialog box under the Calibration
Tab.
C2 Calibration
C2 calibration requires C2 load sensors. (For scales without C2 load sensors see Hard
Calibration below). The Weigh Module reads the performance characteristics of the
individual load cells and detects the quantity of load cell(s) in the system. C2 Calibration
can be performed by pressing “THE BUTTON” located in the front panel of the module,
or via Allen Bradley RS LOGIX 5000 using either the output table or ladder logic.