Technical data

Chapter 9 – Communications
Siemens Building Technologies, Inc. 81
Additional display points on the SED2 drive that may be of use:
• INVERTER VER (Point 83); the SED2 firmware version number
• DRIVEMODEL (Point 84); the STB drive model number
Supervisory Control – This is the most typical application. The sensor for the control variable
(water temperature) is hard-wired to the SED2 and the built-in SED2 control loop (PI loop macro
must be enabled during drive setup) modulates the control device (fan). Change Point 64
(Parameter P2200) to 1 to enable PID control. When using the SED2 PID mode, you will need to
program other parameters depending on the application circumstances. These parameters
include PID system gain, integral, and differential adjustment to stabilize the PID control system
for the application. Set these parameters during SED2 commissioning. For examples of the PID
loop macro, see other sections in this User Manual.
When using this strategy, the point to unbundle and command for the setpoint is FREQ REF
(Point 51). FREQ REF (Point 51) has a slope of 0.006103516, which corresponds to a value of
16384 (4000h)=100%.
Unbundle PI FEEDBACK (Point 60) to monitor the control variable (water temperature). These
points are provided with units of percent, where 0% and 100% correspond to the range of the
sensor that measures the control variable. Therefore, if you want to read in the proper units of the
controlled variable (such as degrees Fahrenheit, WC), unbundle the setpoint with the appropriate
slope and intercept from the point database:
×
×
(Desired Range) (Slope of Existing Point)
New Slope =
Range of Existing Point
(60 - 0 HZ) (0.01)
= = 0.006
100 - 0 %
The new intercept equals the lowest value of the desired range.
Example: The following example illustrates this conversion procedure.
You are controlling water temperature from a cooling tower using the SED2 to control a fan. The
temperature sensor has a range of 30 to 250 degrees Fahrenheit.
To unbundle the setpoint (FREQ REF), for commanding in degrees Fahrenheit, where 0 to 60 Hz
is equal to 30 to 250 degrees Fahrenheit:
New Intercept = 30 (the temperature that corresponds to 0%)
New Slope = (Desired Range) × (Slope of Existing Point)
Range of Existing Point
= (250 - 30 degrees Fahrenheit) × (0.006103516)
= 0.01343
100 - 0%
To unbundle the feedback (PI FEEDBACK) for monitoring in degrees Fahrenheit:
New Intercept = 30
New Slope = (Desired Range) × (Slope of Existing Point)
Range of Existing Point
= (250 - 30 degrees Fahrenheit) × (0.01)
= 0.022
100 - 0%