Frequency Signal; Pwm Signal - Danfoss AK-CC55 Water Loop User Manual

AK-CC55 Water Loop
When a cooling demand arises, the requested capacity will increase and as soon as it reaches the set start speed of
45%, the analogue output signal will go to the corresponding start signal (4,5 V) and the compressor will be started
via the relay output. Now the compressor will run at start speed for 10 seconds, before the variable speed control
takes over. From here on, the analogue output signal will vary with the requested capacity of the compressor and
ensure a precise temperature control in the cabinet.
If the requested capacity reaches the defined minimum speed limit of 20%, the compressor will continue to run at
this speed until the requested capacity reaches 0%. At this point, the analogue output will drop to the defined
minimum signal and the compressor will be cut-out via the relay signal.

Frequency signal

The example above also applies for a frequency control signal.

PWM signal

The PWM signal is a Pulse Width Modulated signal with a fixed frequency, where the duty cycle is modulated from 0
– 100%. Variable speed brine pumps are often controlled via a PWM signal and the capacity signal is normally
inverted, meaning that a high pump speed corresponds to a low duty cycle of the PWM signal. Therefore, the
analogue output signal provides the option for inverting the output signal.
A capacity curve could look like shown in
Figure 19: Capacity curve
PWM duty cycle%
PWM = 0%
Speed = 1000 RPM
Speed = 150 RPM
Speed = 100 RPM
PWM = 100%
Speed = 0 RPM
c46 Min speed c47 Start speed
10% 15%
Pump
Example:
o09 AO1 signal type = PWM
P97 AO1 PWM frequency = 200Hz
P98 AO1 invert signal = Yes
C46 min. speed = 10%
C47 start speed = 15%
C48 max. speed = 90%
When a cooling demand arises, the requested capacity will increase and as soon as it reaches the set start speed of
15%, the PWM duty cycle will go to the corresponding start signal (85% duty cycle = 150 rpm) and the pump will be
started via the relay output. Now the pump will run at start speed for 10 seconds before the variable speed control
takes over. From here on, the PWM signal will vary with the requested capacity of the pump and ensure a precise
temperature control in the cabinet.
If the requested capacity reaches the defined minimum speed limit of 10% (90% duty cycle = 100 rpm), the pump
will continue to run at this speed until the requested capacity reaches 0%. At this point, the PWM signal will go to a
duty cycle of 100% equal to 0% capacity and the pump will be cut-out via the relay signal.
Oil return management
If the variable speed compressor is running with a low speed for a long period, there is a risk that oil will be trapped
© Danfoss | Climate Solutions | 2022.04
Figure 19.
1000 RPM
100 RPM
Requested
c48 Max speed
90% capacity
BC378540472015en-000101 | 14