Sensoray 518 - Manual (Page 50)

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Many gage installations achieve zero and span calibration with the aid of gage simulation
signals. Each gage produces three signals that are multiplexed onto a single 518 input channel.
One signal is the load signal (L), representing the real load. The other two are simulated load
signals, one for a zero load (Z) and the other a full load (F) condition. In the following
discussion, the symbolic names L, Z, and F are used to reference either physical or simulated
loads (whichever you are using to calibrate your gage with).
During normal operation, the L signal is applied to the 518 input channel. When it is time to
calibrate the gage zero and span, the following procedure is used:
1. The Z signal is connected to the input channel, and the host sends a Set Gage Zero
command to the 518. This establishes the gage zero load condition.
2. The F signal is connected to the input channel, and the host sends a Set Gage Span
command to the 518. The corresponding full load count is downloaded to the 518 as
part of this command to establish the gage full load condition.
Once the above procedure has been completed, the gage calibration may be read from the
coprocessor via the Read Gage Calibration command. The six bytes returned by this command
may be saved for future use.
The next time the gage is to be calibrated, either method may be used (even if the coprocessor
has just been reset or powered up). If gage calibration via the Set Gage Zero and Set Gage Span
commands is a problem in your application, you may opt to calibrate the gage using the Set Gage
Calibration command.
Taring
In many gaging applications, it is necessary to measure the weight of material within a container.
This is done by first weighing the empty container to determine its tare weight.
The 518 is designed to tare loads and automatically deduct the tare weight from all subsequent
output data to the host processor. Assuming that a gage has been calibrated for zero and span, a
load may be tared as follows:
1. Position the empty container onto the load cell assembly.
2. Issue a Tare Gage command from to the 518 coprocessor.