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Slope and Intercept Con ersion
Several drive parameters are available for monitoring purposes. The available parameters 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.
Dri e Controlled Feedbac
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 built into the drive. The setpoint for the control
variable (water temperature set point) is unbundled and commanded by the field panel, based on the 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 formulas allow the user to define a new slope and intercept to convert the unit.
Con ersion E ample
The drive is controlling a fan, which in turn is controlling the water temperature from a cooling tower. The temperature sensor
has a range of -1 °C to +121 °C (30 °F to 250 °F). To unbundle the set point (INPUT REF 1), for commanding in degrees
Fahrenheit, where 0 to 60 Hz is equal to -1 °C to +121 °C: New Intercept = 30 (the temperature that corresponds to 0%)
1. Desired Range = Range Maximum – Range Minimum
Note:
2. Range of Existing Point = Existing Range Maximum – Existing Range Minimum
Field Panel Controlled Feedbac
In this strategy, the sensor is connected to the APOGEE FLN network at a remote location, and the control loop is executed
in PPCL. The drive speed command is passed from the field panel to the drive by commanding INPUT REF 1 (Point 60).
NO ICE Damage to Equipment. This strategy is not recommended because it means that the loop is being closed over the network. Delays
due to processor scan time and network traffic can cause control to be degraded or lost and damage to HVAC equipment may result.
(Desired Range) x (Slope of Existing Point)
New Slope =
(Range of Existing Point)
(60 - 0) Hz x (0.01)
New Slope =
(100 - 0)%
(Desired Range) x (Slope of Existing Point)
New Slope =
(Range of Existing Point)
(250 - 30) °F x (0.1)
New Slope =
(100 - 0)%
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Slope and Intercept Con ersion
= 0.006
= 0.22
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