Yaskawa E7 Apogee FLN - Manual (Page 21)

APOGEE FLN Strategies 3-3
Slope and Intercept Conversion
Several drive parameters are available for monitoring purposes. These include FREQ OUTPUT (Point 3), SPEED (Point 5), CURRENT
(Point 6), TORQUE (Point 7), POWER (Point 8), DRIVE TEMP (Point 9), KWH (Point 10), and RUN TIME (Point 12). These points can
be unbundled for monitoring or used in various global control strategies.
! Drive Controlled Feedback
The most typical application is Supervisory Control. The sensor for the control variable (e.g., water temperature) is hard-wired to the drive
and the control device (fan) is modulated using the PI control loop that is built into the drive. The setpoint for the control variable (water
temperature set point) is unbundled and commanded by the field panel, based on some building control strategy implemented in PPCL.
When this strategy is used, the point to unbundle and command for the set point is INPUT REF 1 (Point 60). The control variable
(e.g., water temperature) can be monitored by unbundling PI FEEDBACK (Point 62). These points are provided in units of percent, where
0% and 100% correspond to the range of the sensor being used to measure the control variable. These points have default units in Hz.
If other units are required, unbundle these points with appropriate slopes and intercepts. The new intercept will be equal to the lowest value
of the desired range. The following formula lets you define a new slope and intercept in order to accomplish the unit conversion.
New Slope = (60 - 0)Hz x (0.01)
(100 - 0)%
= 0.006
New Slope = (Desired Range) x (Slope of Existing Point)
(Range of Existing Point)
Conversion Example
You are controlling water temperature from a cooling tower using the drive to control a fan. The temperature sensor has a range
of 30
o F to 250 o F. To unbundle the set point (INPUT REF 1), for commanding in degrees Fahrenheit, where 0 to 60 Hz is equal to
30 o F to 250 o F:
New Intercept = 30 (the temperature that corresponds to 0%)
New Slope = (250 - 30)°F x (0.1)
(100 - 0)%
= 0.22
New Slope = (Desired Range) x (Slope of Existing Point)
(Range of Existing Point)
Formula Notes:
Desired Range = Range Maximum – Range Minimum
Range of Existing Point = Existing Range Maximum – Existing Range Minimum