Analog Velocity Scaling

To have any useful meaning, the Voltage or Current from an analog transducer must be scaled to measurement units. This topic describes how to manually calculate the Scaling and Offset parameters for an analog velocity input.

Delta Recommends using the Scale/Offset Wizard for scaling the velocity. If you need to do it manually, read this topic.

Scaling Voltage or Current to Velocity Units for Tachometers

The RMC calculates the Actual Velocity from the tachometer voltage every control-loop time using either of the following formulas:

Actual Velocity = (Voltage + Velocity Offset) x Velocity Scale

Actual Velocity = (Current + Velocity Offset) x Velocity Scale

Calculating the Velocity Scale and Offset

From the tachometer specification sheet, determine the voltage or current at which the velocity is zero. Call it VZERO or CZERO. Or, for greater accuracy, make sure the tachometer is stopped, then look at the voltage or current feedback value in the Status Registers pane. Call this value Call it VZERO or CZERO.
Negate VZERO or CZERO and enter it as the Velocity Offset:

Velocity Offset = -VZERO

Velocity Offset = -CZERO
From the tachometer specification sheet, determine what the maximum velocity is. Call it Max Vel.
From the tachometer specification sheet, determine what the voltage or current output should be at the Max Vel. Call it VMAX or CMAX. Calculate the Velocity Scale with one of the following equations:

Velocity Scale = Max Vel / (VMAX - VZERO)

Velocity Scale = Max Vel / (CMAX - CZERO)