Delta RMC151 - Manual (Page 35)

2 Starting Up the RMC
2.2.4. Analog Acceleration Scaling
To have any useful meaning, the Voltage or Current from an analog transducer on an
acceleration input must be scaled to acceleration units. This topic describes how to manually
calculate the Scaling and Offset parameters for an analog acceleration transducer.
Notice that Acceleration inputs are only used in advanced applications.
Scaling Acceleration Units
The RMC calculates the Actual Acceleration every control-loop time using the following
formula:
Actual Acceleration = ((Voltage or Current) + Acceleration Offset) x Acceleration
Scale
Calculating the Acceleration Scale and Offset
1. From the accelerometer specification sheet, determine the voltage or current at which
the acceleration is zero. Call it V
ZERO
or C
ZERO
. Negate that value, and enter it as the
Acceleration Offset.
Acceleration Offset = -V
ZERO
Acceleration Offset = -C
ZERO
2. From the accelerometer specification sheet, determine what the maximum
acceleration is. Call it Max Accel.
3. From the accelerometer specification sheet, determine what the voltage or current
output should be at the Max Accel. Call it V
MAX
or C
MAX
. Calculate the Acceleration Scale
with one of the following equations:
Acceleration Scale = Max Accel / (V
MAX
- V
ZERO
)
Acceleration Scale = Max Accel / (C
MAX
- C
ZERO
)
1.
2.2.5. Analog Pressure or Force Scaling
To have any useful meaning, the Voltage or Current from the analog pressure or force
transducer must be scaled to pressure or force units. The Pressure/Force Scale,
Pressure/Force Offset, and Invert Feedback Polarity parameters are used to define pressure or
force units as a function of transducer voltage. This topic describes how to manually calculate
these parameters for an analog pressure transducer.
Delta Recommends using the Scale/Offset Wizard for scaling the pressure or force. If you need
to do it manually, read this topic.
Scaling Single-Input Pressure or Force
The RMC calculates the Actual Pressure/Force every control-loop using the following
formula (may be either pressure or force):
Actual Pressure = (Voltage (or Current) x Pressure Scale) + Pressure Offset
To correctly scale the axis for your particular application, use one of the methods below to
find the Pressure/Force Scale and Pressure/Force Offset parameters.
Method 1: Use Transducer Specifications
• From the transducer data sheet, find the maximum output voltage of your pressure
transducer and the pressure at that voltage.
• Calculate the Pressure Scale with the following formula:
Pressure Scale = Max Pressure / Max Voltage
• Make sure the system has 0 pressure and then record the value of the Voltage
register. Enter the negative of that value as the Pressure Offset.
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