Sutron Corporation 8310 & 7310 Users Manual 8800-1125Rev. 2.7 (BETA) 4/16/2014 pg. 177
A 5 psi pressure sensor has a calibrated span of 36.22 millivolts and an offset of -1.22 mv. This
example gives all the information necessary, but is in a different form. We know that (x1, y1) = (-
1.22, 0). We know that Y2 is 5 psi but they do not give us the X2 value. Instead they give the
span from which we can compute X2 knowing that X2 = Span + X1. Or we can just use the span
as it is = X2 - X1. So we have Slope = (Y2-Y1)/(X2-X1) = (5-0)/0.03622) = 138.04 and offset = 0 - (-
0.00122) * slope = 0.168. Notice that we converted the millivolts to volts before using the values
in the equation because the x values must be in the same units as the raw reading.
Let Calibrate Compute the Slope and Offset for you
The 8310 calibrate function built into the 8310 can compute the slope and offset for you. In
order to use the calibration function, you will need to have an independent measurement for
the input or a way to force the input to a known value. Calibration process supports both single
point calibrations where only the offset is determined or two point calibrations where both the
slope and offset are determined. The calibrate function is available from any menu displaying
an input such as in Station Setup/Measurements or Diagnostic/Inputs Calibration.
Printing the Setup
To print an 8310 setup, use the LIST command.
Understand the Measurement process
The 8310 uses the fields entered in Station Setup/Measurements to control when it measures
and averages data from sensors. This section gives a more complete description of how all the
measurements are made.
The 8310 uses separate processes to make each measurement in the system.
Multiple processes can be running in parallel so that all measurements are made as
efficiently as possible.
The measurement process starts at the time designated by the MeasTime and
MeasInterval.
The process will first will use the switched power settings to see if the sensor needs to
be turned on and warmed up in order to make the measurement. Warmup times add
to the time needed to complete the measurement.
Processes then gain access to resources (like the analog module) on a first come-first
serve basis.
Processes will have to wait for each other if they both need the same resource.
If one process needs the identical measurement as another process (same config and
time), that measurement is shared between the processes.
Measurements are time-stamped with the time of the measurement even though that
measurement may have taken several seconds (or even minutes) to be made.
When averaging, the processing implements a few additional steps:
The system times the sampling so the last sample is taken at the measurement time.
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