This Design Guide is intended for qualified personnel, such as:
•
Project and systems engineers.
•
Design consultants.
•
Application and product specialists.
The Design Guide provides technical information to understand the capabilities of the VLT® Flow Drive FC 111 for integration into
motor control and monitoring systems. Its purpose is to provide design considerations and planning data for integration of the
drive into a system. It caters for selection of drives and options for a diversity of applications and installations. Reviewing the detailed product information in the design stage enables developing a well-conceived system with optimal functionality and efficiency.
This manual is targeted at a worldwide audience. Therefore, wherever occurring, both SI and imperial units are shown.
VLT® is a registered trademark for Danfoss A/S.
1.2 Additional Resources
1.2.1 Other Resources
Other resources are available to understand advanced drive functions and programming.
•
VLT® Flow Drive FC 111 Operating Guide provides basic information on mechanical dimensions, installation, and programming.
•
VLT® Flow Drive FC 111 Programming Guide provides information on how to program, and includes complete parameter descriptions.
•
Danfoss VLT® Energy Box software. Select PC Software Download at
VLT® Energy Box software allows energy consumption comparisons of HVAC fans and pumps driven by Danfoss drives and alternative methods of flow control. Use this tool to accurately project the costs, savings, and payback of using Danfoss drives on HVAC
fans, pumps, and cooling towers.
Supplementary publications and manuals are available from Danfoss website www.danfoss.com.
www.danfoss.com.
1.2.2 MCT 10 Set-up Software Support
Download the software from the service and support section on www.danfoss.com.
During the installation process of the software, enter access code 81462700 to activate the VLT® Flow Drive FC 111 functionality. A
license key is not required for using the VLT® Flow Drive FC 111 functionality.
The latest software does not always contain the latest updates for drives. Contact the local sales office for the latest drive updates (in
the form of *.OSS files).
1.3 Document and Software Version
This guide is regularly reviewed and updated. All suggestions for improvement are welcome.
The original language of this manual is English.
Table 1: Document and Software Version
1.4 Regulatory Compliance
1.4.1 Introduction
AC drives are designed in compliance with the directives described in this section.
1.4.2 CE Mark
The CE mark (Communauté Européenne) indicates that the product manufacturer conforms to all applicable EU directives. The EU
directives applicable to the design and manufacture of drives are listed in the following table.
The CE mark does not regulate the quality of the product. Technical specifications cannot be deduced from the CE mark.
N O T I C E
Drives with an integrated safety function must comply with the machinery directive.
Table 2: EU Directives Applicable to Drives
Declarations of conformity are available on request.
1.4.2.1 Low Voltage Directive
The aim of the Low Voltage Directive is to protect persons, domestic animals and property against dangers caused by the electrical
equipment, when operating electrical equipment that is installed and maintained correctly, in its intended application. The directive
applies to all electrical equipment in the 50–1000 V AC and the 75–1500 V DC voltage ranges.
1.4.2.2 EMC Directive
The purpose of the EMC (electromagnetic compatibility) Directive is to reduce electromagnetic interference and enhance immunity
of electrical equipment and installations. The basic protection requirement of the EMC Directive states that devices that generate
electromagnetic interference (EMI), or whose operation could be affected by EMI, must be designed to limit the generation of electromagnetic interference and shall have a suitable degree of immunity to EMI when properly installed, maintained, and used as
intended. Electrical equipment devices used alone or as part of a system must bear the CE mark. Systems do not require the CE
mark, but must comply with the basic protection requirements of the EMC Directive.
1.4.2.3 ErP Directive
The ErP Directive is the European Ecodesign Directive for energy-related products. The directive sets ecodesign requirements for
energy-related products, including drives, and aims at reducing the energy consumption and environmental impact of products by
establishing minimum energy-efficiency standards.
Indicates a hazardous situation which, if not avoided, will result in death or serious injury.
W A R N I N G
Indicates a hazardous situation which, if not avoided, could result in death or serious injury.
C A U T I O N
Indicates a hazardous situation which, if not avoided, could result in minor or moderate injury.
N O T I C E
Indicates information considered important, but not hazard-related (for example, messages relating to property damage).
Safety
2.2 Qualified Personnel
To allow trouble-free and safe operation of the unit, only qualified personnel with proven skills are allowed to transport, store, assemble, install, program, commission, maintain, and decommission this equipment.
Persons with proven skills:
•
Are qualified electrical engineers, or persons who have received training from qualified electrical engineers and are suitably
experienced to operate devices, systems, plant, and machinery in accordance with pertinent laws and regulations.
•
Are familiar with the basic regulations concerning health and safety/accident prevention.
•
Have read and understood the safety guidelines given in all manuals provided with the unit, especially the instructions given in
the Operating Guide.
•
Have good knowledge of the generic and specialist standards applicable to the specific application.
2.3 Safety Precautions
W A R N I N G
HAZARDOUS VOLTAGE
AC drives contain hazardous voltage when connected to the AC mains or connected on the DC terminals. Failure to perform
installation, start-up, and maintenance by skilled personnel can result in death or serious injury.
Only skilled personnel must perform installation, start-up, and maintenance.
-
W A R N I N G
UNINTENDED START
When the drive is connected to AC mains, DC supply, or load sharing, the motor may start at any time. Unintended start during
programming, service, or repair work can result in death, serious injury, or property damage. Start the motor with an external
switch, a fieldbus command, an input reference signal from the local control panel (LCP), via remote operation using MCT 10
software, or after a cleared fault condition.
Disconnect the drive from the mains.
-
Press [Off/Reset] on the LCP before programming parameters.
-
Ensure that the drive is fully wired and assembled when it is connected to AC mains, DC supply, or load sharing.
3.1.1 Why Use a Drive for Controlling Fans and Pumps?
A drive takes advantage of the fact that centrifugal fans and pumps follow the laws of proportionality for such fans and pumps. For
further information, see 3.1.1.2 Example of Energy Savings.
3.1.1.1 The Clear Advantage - Energy Savings
The clear advantage of using a drive for controlling the speed of fans or pumps lies in the electricity savings.
When comparing with alternative control systems and technologies, a drive is the optimum energy control system for controlling
fan and pump systems.
Illustration 1: Fan Curves (A, B, and C) for Reduced Fan Volumes
Illustration 2: Energy Savings with Drive Solution
When using a drive to reduce fan capacity to 60% - more than 50% energy savings may be obtained in typical applications.
3.1.1.2 Example of Energy Savings
As shown in the following illustration, the flow is controlled by changing the RPM. By reducing the speed by only 20% from the
rated speed, the flow is also reduced by 20%. This is because the flow is directly proportional to the RPM. The consumption of electricity, however, is reduced by 50%.
If the system in question only needs to be able to supply a flow that corresponds to 100% a few days in a year, while the average is
below 80% of the rated flow for the remainder of the year, the amount of energy saved is even more than 50%.
The following illustration describes the dependence of flow, pressure, and power consumption on RPM.
Illustration 3: Laws of Proportionally
Q
n
1
1
Flow:
Pressure:
Power:
Table 4: The Laws of Proportionality
=
Q
n
2
2
H
1
=
H
2
P
1
=
P
2
2
n
1
n
2
3
n
1
n
2
3.1.1.3 Comparison of Energy Savings
The Danfoss drive solution offers major savings compared with traditional energy saving solutions such as discharge damper solution and inlet guide vanes (IGV) solution. This is because the drive is able to control fan speed according to thermal load on the
system, and the drive has a built-in facility that enables the drive to function as a building management system, BMS.
The illustration in 3.1.1.2 Example of Energy Savings shows typical energy savings obtainable with 3 well-known solutions when fan
volume is reduced to 60%. As the graph shows, more than 50% energy savings can be achieved in typical applications.
Illustration 4: The 3 Common Energy Saving Systems
Illustration 5: Energy Savings
Discharge dampers reduce power consumption. Inlet guide vanes offer a 40% reduction, but are expensive to install. The Danfoss
drive solution reduces energy consumption with more than 50% and is easy to install. It also reduces noise, mechanical stress, and
wear-and-tear, and extends the life span of the entire application.
This example is calculated based on pump characteristics obtained from a pump datasheet. The result obtained shows energy savings of more than 50% at the given flow distribution over a year. The payback period depends on the price per kWh and the price of
drive. In this example, it is less than a year when compared with valves and constant speed.
If a drive is used for controlling the flow or pressure of a system, improved control is obtained.
A drive can vary the speed of the fan or pump, obtaining variable control of flow and pressure. Furthermore, a drive can quickly
adapt the speed of the fan or pump to new flow or pressure conditions in the system.
Simple control of process (flow, level, or pressure) utilizing the built-in PI control.
3.1.1.6 Star/Delta Starter or Soft Starter not Required
When larger motors are started, it is necessary in many countries to use equipment that limits the start-up current. In more traditional systems, a star/delta starter or soft starter is widely used. Such motor starters are not required if a drive is used.
As shown in the following illustration, a drive does not consume more than rated current.
Illustration 8: Start-up Current
3.1.1.7 Using a Drive Saves Money
The example in 3.1.1.8 Traditional Fan System without a Drive and 3.1.1.9 Fan System Controlled by Drives shows that a drive replaces other equipment. It is possible to calculate the cost of installing the 2 different systems. In the example, the 2 systems can be
established at roughly the same price.
Use the VLT® Energy Box software that is introduced in chapter Additional Resources to calculate the cost savings that can be achieved by using a drive.
The following sections give typical examples of applications.
3.1.2.1 Variable Air Volume
VAV or variable air volume systems, control both the ventilation and temperature to satisfy the requirements of a building. Central
VAV systems are considered to be the most energy efficient method to air condition buildings. By designing central systems instead
of distributed systems, a greater efficiency can be obtained.
The efficiency comes from utilizing larger fans and larger chillers which have much higher efficiencies than small motors and distributed air-cooled chillers. Savings are also seen from the decreased maintenance requirements.
The VLT Solution
While dampers and IGVs work to maintain a constant pressure in the ductwork, a drive solution saves much more energy and reduces the complexity of the installation. Instead of creating an artificial pressure drop or causing a decrease in fan efficiency, the
drive decreases the speed of the fan to provide the flow and pressure required by the system.
Centrifugal devices such as fans behave according to the centrifugal laws. This means that the fans decrease the pressure and flow
they produce as their speed is reduced. Their power consumption is thereby significantly reduced. The PI controller of the drive can
be used to eliminate the need for additional controllers.
CAV, or constant air volume systems, are central ventilation systems usually used to supply large common zones with the minimum
amounts of fresh tempered air. They preceded VAV systems and are therefore found in older multi-zoned commercial buildings as
well. These systems preheat amounts of fresh air utilizing air handling units (AHUs) with a heating coil, and many are also used to air
condition buildings and have a cooling coil. Fan coil units are frequently used to assist in the heating and cooling requirements in
the individual zones.
The VLT Solution
With a drive, significant energy savings can be obtained while maintaining decent control of the building. Temperature sensors or
CO2 sensors can be used as feedback signals to drives. Whether controlling temperature, air quality, or both, a CAV system can be
controlled to operate based on actual building conditions. As the number of people in the controlled area decreases, the need for
fresh air decreases. The CO2 sensor detects lower levels and decreases the supply fans speed. The return fan modulates to maintain
a static pressure setpoint or fixed difference between the supply and return airflows.
With temperature control, especially used in air conditioning systems, as the outside temperature varies as well as the number of
people in the controlled zone changes, different cooling requirements exist. As the temperature decreases below the setpoint, the
supply fan can decrease its speed. The return fan modulates to maintain a static pressure setpoint. By decreasing the air flow, energy used to heat or cool the fresh air is also reduced, adding further savings.
Several features of the Danfoss dedicated drive can be utilized to improve the performance of the CAV system. One concern of
controlling a ventilation system is poor air quality. The programmable minimum frequency can be set to maintain a minimum
amount of supply air regardless of the feedback or reference signal. The drive also includes a PI controller, which allows monitoring
both temperature and air quality. Even if the temperature requirement is fulfilled, the drive maintains enough supply air to satisfy
the air quality sensor. The controller is capable of monitoring and comparing 2 feedback signals to control the return fan by maintaining a fixed differential airflow between the supply and return ducts as well.
Cooling tower fans cool condenser-water in water-cooled chiller systems. Water-cooled chillers provide the most efficient means of
creating chilled water. They are as much as 20% more efficient than air cooled chillers. Depending on climate, cooling towers are
often the most energy efficient method of cooling the condenser-water from chillers.
They cool the condenser water by evaporation. The condenser water is sprayed into the cooling tower until the cooling towers fill to
increase its surface area. The tower fan blows air through the fill and sprayed water to aid in the evaporation. Evaporation removes
energy from the water dropping its temperature. The cooled water collects in the cooling towers basin where it is pumped back
into the chillers condenser and the cycle is repeated.
The VLT Solution
With a drive, the cooling towers fans can be controlled to the required speed to maintain the condenser-water temperature. The
drives can also be used to turn the fan on and off as needed.
Several features of the Danfoss dedicated drive can be utilized to improve the performance of cooling tower fans applications. As
the cooling tower fans drop below a certain speed, the effect the fan has on cooling the water becomes small. Also, when utilizing a
gearbox to frequency control the tower fan, a minimum speed of 40–50% is required.
The customer programmable minimum frequency setting is available to maintain this minimum frequency even as the feedback or
speed reference calls for lower speeds.
Also as a standard feature, the drive can be programmed to enter a sleep mode and stop the fan until a higher speed is required.
Additionally, some cooling tower fans have undesirable frequencies that may cause vibrations. These frequencies can easily be avoided by programming the bypass frequency ranges in the drive.
Condenser water pumps are primarily used to circulate water through the condenser section of water cooled chillers and their associated cooling tower. The condenser water absorbs the heat from the chiller's condenser section and releases it into the atmosphere
in the cooling tower. These systems are used to provide the most efficient means of creating chilled water, they are as much as 20%
more efficient than air cooled chillers.
The VLT Solution
Drives can be added to condenser water pumps instead of balancing the pumps with a throttling valve or trimming the pump impeller.
Using a drive instead of a throttling valve simply saves the energy that would have been absorbed by the valve. This can amount to
savings of 15–20% or more. Trimming the pump impeller is irreversible, thus if the conditions change and higher flow is required
the impeller must be replaced.
Primary pumps in a primary/secondary pumping system can be used to maintain a constant flow through devices that encounter
operation or control difficulties when exposed to variable flow. The primary/secondary pumping technique decouples the primary
production loop from the secondary distribution loop. This allows devices such as chillers to obtain constant design flow and operate properly while allowing the rest of the system to vary in flow.
As the evaporator flow rate decreases in a chiller, the chilled water begins to become overchilled. As this happens, the chiller attempts to decrease its cooling capacity. If the flow rate drops far enough, or too quickly, the chiller cannot shed its load sufficiently
and the chiller’s safety trips the chiller requiring a manual reset. This situation is common in large installations especially when 2 or
more chillers in parallel are installed if primary/ secondary pumping is not utilized.
The VLT Solution
Depending on the size of the system and the size of the primary loop, the energy consumption of the primary loop can become
substantial.
A drive can be added to the primary system to replace the throttling valve and/or trimming of the impellers, leading to reduced
operating expenses. 2 control methods are common:
Flow meter
Because the desired flow rate is known and is constant, a flow meter installed at the discharge of each chiller, can be used to control
the pump directly. Using the built-in PI controller, the drive always maintains the appropriate flow rate, even compensating for the
changing resistance in the primary piping loop as chillers and their pumps are staged on and off.
Local speed determination
The operator simply decreases the output frequency until the design flow rate is achieved.
Using a drive to decrease the pump speed is very similar to trimming the pump impeller, except it does not require any labor, and
the pump efficiency remains higher. The balancing contractor simply decreases the speed of the pump until the proper flow rate is
achieved and leaves the speed fixed. The pump operates at this speed any time the chiller is staged on. Because the primary loop
does not have control valves or other devices that can cause the system curve to change, and the variance due to staging pumps
and chillers on and off is usually small, this fixed speed remains appropriate. If the flow rate needs to be increased later in the system’s life, the drive can simply increase the pump speed instead of requiring a new pump impeller.
Secondary pumps in a primary/secondary chilled water pumping system distribute the chilled water to the loads from the primary
production loop. The primary/secondary pumping system is used to hydronically de-couple 1 piping loop from another. In this case,
the primary pump is used to maintain a constant flow through the chillers while allowing the secondary pumps to vary in flow,
increase control and save energy.
If the primary/secondary concept is not used in the design of a variable volume system when the flow rate drops far enough or too
quickly, the chiller cannot shed its load properly. The chiller’s low evaporator temperature safety then trips the chiller requiring a
manual reset. This situation is common in large installations especially when 2 or more chillers in parallel are installed.
The VLT Solution
While the primary-secondary system with 2-way valves improves energy savings and eases system control problems, the true energy savings and control potential is realized by adding drives.
With the proper sensor location, the addition of drives allows the pumps to vary their speed to follow the system curve instead of
the pump curve. This results in the elimination of wasted energy and eliminates most of the overpressurization that 2-way valves
can be subjected to.
As the monitored loads are reached, the 2-way valves close down. This increases the differential pressure measured across the load
and the 2-way valve. As this differential pressure starts to rise, the pump is slowed to maintain the control head also called setpoint
value. This setpoint value is calculated by summing the pressure drop of the load and the 2-way valve together under design conditions.
N O T I C E
When running multiple pumps in parallel, they must run at the same speed to maximize energy savings, either with individual
dedicated drives or 1 drive running multiple pumps in parallel.
In the pump application system, a damaged check valve is hard to detect, which therefore causes low efficiency of the whole system. VLT® Flow Drive FC 111 has the ability to monitor the status of check valves in the system. After enabling the check valve monitoring function via setting the parameter 22-04 Check Valve Monitor to [1] Enabled, once a damaged check valve is detected, the
drive trips warning 159, Check Valve Failure.
3.1.4 Dry Pump Detection
In the pump application system, the drive monitors the operation status of the system to detect whether there is water on pump's
suction side. If the pump runs at maximum speed and consumes little power, then it can be assumed that there is no water on the
pump's suction side. Via setting the parameter 22-26 Dry Pump Function to warning or alarm, once the dry pump condition is detected, the drive trips warning/alarm 93, dry pump.
3.1.5 End of Curve Detection
In the pump application system, the drive monitors the operation status of the system to detect whether the pressure side of pump
is subject to a major leakage. If the pump runs at maximum speed for a defined time period, but the pressure is below the set point,
then it can be considered to reflect the end of curve situation. Via setting the parameter 22-50 End of Curve Function to warning or
alarm, once the end of curve condition is detected, the drive trips warning/alarm 94, end of curve.
3.1.6 Time-based Functions
In some application scenarios, there are requirements to control the motor running for a specific time, in a specific direction and a
specific speed within a specific time interval. For example, checking the motor status in fire mode or exercising pumps, fans, and
compressors.
For detailed parameter settings, refer to the parameter group 23-** Time-based Functions in the drive's Programming Guide.
3.2 Control Structures
3.2.1 Introduction
There are two control modes for the drive:
Open loop.
•
Closed loop.
•
Select [0] Open loop or [1] Closed loop in parameter 1-00 Configuration Mode.
In the configuration shown in the above illustration, parameter 1-00 Configuration Mode is set to [0] Open loop. The resulting reference from the reference handling system or the local reference is received and fed through the ramp limitation and speed limitation
before being sent to the motor control. The output from the motor control is then limited by the maximum frequency limit.
3.2.3 PM/EC+ Motor Control
The Danfoss EC+ concept provides the possibility for using high-efficient PM motors (permanent magnet motors) in IEC standard
enclosure sizes operated by Danfoss drives.
The commissioning procedure is comparable to the existing one for asynchronous (induction) motors by utilizing the Danfoss VVC
PM control strategy.
Customer advantages:
•
Free choice of motor technology (permanent magnet or induction motor).
•
Installation and operation as know on induction motors.
•
Manufacturer independent when selecting system components (for example, motors).
•
Best system efficiency by selecting best components.
•
Possible retrofit of existing installations.
•
Power range: 0.37–90 kW (0.5–121 hp) (400 V) for induction motors and 0.37–22 kW (0.5–30 hp) (400 V) for PM motors.
Current limitations for PM motors:
•
Currently only supported up to 22 kW (30 hp).
•
LC filters are not supported with PM motors.
•
Kinetic back-up algorithm is not supported with PM motors.
•
Support only complete AMA of the stator resistance Rs in the system.
•
No stall detection (supported from software version 62.80).
3.2.4 Local (Hand On) and Remote (Auto On) Control
The drive can be operated manually via the local control panel (LCP) or remotely via analog/digital inputs or serial bus. If allowed in
parameter 0-40 [Hand on] Key on LCP, parameter 0-44 [Off/Reset] Key on LCP, and parameter 0-42 [Auto on] Key on LCP, it is possible to
start and stop the drive via LCP by pressing [Hand On] and [Off/Reset]. Alarms can be reset via the [Off/Reset] key.
+
Illustration 18: LCP Keys
Local reference forces the configuration mode to open loop, independent on the setting of parameter 1-00 Configuration Mode.
The internal controller allows the drive to become a part of the controlled system. The drive receives a feedback signal from a sensor
in the system. It then compares this feedback to a setpoint reference value and determines the error, if any, between these 2 signals.
It then adjusts the speed of the motor to correct this error.
For example, consider a compressor application where the speed of the compressor is to be controlled to ensure a constant suction
pressure in an evaporator. The suction pressure value is supplied to the drive as the setpoint reference. A pressure sensor measures
the actual suction pressure in the evaporator and supplies the data to the drive as a feedback signal. If the feedback signal is greater
than the setpoint reference, the drive speeds up the compressor to reduce the pressure. In a similar way, if the suction pressure is
lower than the setpoint reference, the drive automatically slows down the compressor to increase the pressure.
Illustration 19: Control Structure Closed Loop
While the default values for the closed-loop controller of the drive often provide satisfactory performance, the control of the system
can often be optimized by adjusting parameters.
3.2.6 Feedback Conversion
In some applications, it may be useful to convert the feedback signal. One example of this is using a pressure signal to provide flow
feedback. Since the square root of pressure is proportional to flow, the square root of the pressure signal yields a value proportional
to the flow. See the following illustration.
External references (analog inputs and serial communication bus references).
•
The preset relative reference.
•
Feedback-controlled setpoint.
Up to 8 preset references can be programmed in the drive. The active preset reference can be selected using digital inputs or the
serial communications bus. The reference can also be supplied externally, most commonly from an analog input. This external
source is selected by 1 of the 3 reference source parameters (parameter 3-15 Reference 1 Source, parameter 3-16 Reference 2 Source,
and parameter 3-17 Reference 3 Source). All reference resources and the bus reference are added to produce the total external reference. The external reference, the preset reference, or the sum of the 2 can be selected to be the active reference. Finally, this reference can by be scaled using parameter 3-14 Preset Relative Reference.
The scaled reference is calculated as follows:
Reference = X + X ×
Where X is the external reference, the preset reference or the sum of these and Y is parameter 3-14 Preset Relative Reference in [%].
If Y, parameter 3-14 Preset Relative Reference, is set to 0%, the reference is not affected by the scaling.
3.2.8 Tuning the Drive Closed-loop
Once the drive's closed-loop controller has been set up, test the performance of the controller. Often, its performance may be acceptable using the default values of parameter 20-93 PI Proportional Gain and parameter 20-94 PI Integral Time. However, sometimes
it may be helpful to optimize these parameter values to provide faster system response while still controlling speed overshoot.
Set parameter 20-93 PI Proportional Gain to 0.3 and increase it until the feedback signal begins to oscillate. If necessary, start
and stop the drive or make step changes in the setpoint reference to attempt to cause oscillation.
3.
Reduce the PI proportional gain until the feedback signal stabilizes.
4.
Reduce the proportional gain by 40–60%.
5.
Set parameter 20-94 PI Integral Time to 20 s and reduce it until the feedback signal begins to oscillate. If necessary, start and
stop the drive or make step changes in the setpoint reference to attempt to cause oscillation.
Increase the PI integral time until the feedback signal stabilizes.
6.
Increase the integral time by 15–50%.
7.
Product Overview
3.3 Ambient Running Conditions
3.3.1 Air Humidity
The drive has been designed to meet the IEC/EN 60068-2-3 standard, EN 50178 9.4.2.2 at 50 °C (122 °F).
3.3.2 Acoustic Noise or Vibration
If the motor or the equipment driven by the motor - for example, a fan - makes noise or vibrations at certain frequencies, configure
the following parameters or parameter groups to reduce or eliminate the noise or vibrations:
•
Parameter group 4-6* Speed Bypass.
•
Set parameter 14-03 Overmodulation to [0] Off.
•
Switching pattern and switching frequency parameter group 14-0* Inverter Switching.
•
Parameter 1-64 Resonance Dampening.
3.3.2.1 Acoustic Noise
The acoustic noise from the drive comes from 3 sources:
DC-link coils.
•
Integral fan.
•
RFI filter choke.
•
Table 6: Typical Values Measured at a Distance of 1 m (3.28 ft) from the Unit
1
The values are measured under the background of 35 dBA noise and the fan running with full speed.