Hukseflux VU01 User manual

USER MANUAL VU01
Ventilation unit for SR20 and
SR22 pyranometers and IR20 pyrgeometers
Copyright by Hukseflux | manual v1620 | www.huksefluxusa.com | [email protected]

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Warning statements
Always power off the ventilation unit when
conducting maintenance or installing VU01.
VU01 may be used with SR20, SR20-D2, SR22,
SR25, SR25-D1, IR20 & IR20WS sensors. VU01 is
not meant to be used with other pyranometers and
pyrgeometers.
Accidentally exchanging the VU01 cable and sensor
cable will not damage the sensor, but the instrument
and ventilation unit will not function.
In case of cable replacement or extension beyond
5 metres by the user, please note that the voltage
drop across the regular VU01 cable becomes
significant and that a cable with a lower electrical
resistance must be used. Otherwise VU01 may not
get a sufficient amount of power supply. The
ventilator needs a supply between 10.8 and 13.2
VDC, otherwise it may cause damage to the fan.

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Contents
Warning statements 2
Contents 3
List of symbols 4
Introduction 5
1Ordering and checking at delivery 7
1.1 Ordering VU01 7
1.2 Included items 7
1.3 Options 7
1.4 Quick instrument check 7
2Instrument principle and theory 8
3Specifications of VU01 9
3.1 Specifications of VU01 9
3.2 Dimensions of VU01 10
4Standards and recommended practices for use 11
5Installation of VU01 12
5.1 Installation of the ventilation unit 12
5.2 Installation of the sensor 12
5.3 Installation of the VU01 cover 13
5.4 Electrical connection of VU01 14
5.5 Power supply and cable length 15
5.6 Using the status signal for monitoring 17
6Maintenance and trouble shooting 19
6.1 Recommended maintenance 19
6.2 Life expectancy 19
6.3 Trouble shooting 19
7Appendices 21
7.1 Appendix on dust filter replacement 21
7.2 Appendix on tools for VU01 21
7.3 Appendix on spare parts for VU01 21
7.4 Appendix on cable extension / replacement 22
7.5 EC declaration of conformity 23

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List of symbols
Quantities Symbol Unit
Voltage output U V
Electrical resistance R 
Current I A
Time in seconds t s
Rotation rate N 1/min
Supply voltage Usupply V
Voltage drop over cable Udrop V
Fan voltage supply Ufan V
Cable resistance Rcable 
Wire resistance per meter Rewire /m
Cable length Lcable m
Fan current draw Ifan A
Fan status signal high US,high V
Fan status signal low US,low V
Rotation rate treshold Ng1/min

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Introduction
VU01 is a high-quality ventilation unit for use with SR20 and SR22 pyranometers and
IR20 pyrgeometers. Its purpose is to improve the dependability of the measurement.
Measurement accuracy improves because offsets are reduced. Reliability benefits from
prevention of dew and frost formation and quick evaporation and sublimation of water
and snow. ISO/TR 9901 “Solar Energy - Field Pyranometers - Recommended practice for
use” recommends use of ventilators where high accuracy and reliability are required.
VU01 provides an airflow over the instrument body and dome and has two heaters on
board to heat the air. The use of heating (5W or 10W) is optional. The VU01 ventilation
unit runs on 12 VDC voltage. VU01 may be used in combination with Hukseflux’ SR20,
SR20-D2, SR22, SR25 and SR25-D1 secondary standard pyranometers and IR20 and
IR20WS research grade pyrgeometers.
Ventilation promotes thermal equilibrium between all components of radiometers, and
thereby reduces zero offsets. Dew and frost formation is prevented. Additional heating
will promote evaporation of water droplets and sublimation of snow. It should be noted
that heating in combination with pyranometers will lead to increased thermal offsets, so
heating is only recommended if necessary.
Using VU01 is easy. The ventilator is generally used continuously; the heater is typically
controlled by the datalogger. ISO/TR 9901 “Solar Energy - Field Pyranometers -
Recommended practice for use” recommends use of ventilators where high accuracy and
reliability are required. More details can be found in paragraph 5.2.2 and annex A. The
Baseline Surface Radiation Network, BSRN, recommends ventilation for radiometers in its
BSRN operations manual v2.1.
Figure 0.1 VU01 ventilation unit with SR20 secondary standard pyranometer

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VU01 is designed, using high-quality materials, in agreement with the recommendations
of ISO/TR 9901 and BSRN. The footprint of VU01 is small, which prevents accumulation
of snow. The ventilator power is relatively high in order to increase the airflow. The
heaters should be activated using external relays. A fan status signal (high / low) may be
used by the user to monitor rotation of the fan.
For specifications of pyranometers and pyrgeometers and general considerations
concerning site selection and maintenance fur such instruments, please consult the
SR20, SR20-D2, SR22, SR25, SR25-D1 and IR20 manuals.

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1Ordering and checking at delivery
1.1 Ordering VU01
The standard configuration of VU01 is with 5 metres cable. Options are: longer cable (in
multiples of 5 m and a pack of 5 dust filters. Consult Hukseflux for cable options. One
dust filter and one spare dust filter are included with VU01.
1.2 Included items
Arriving at the customer, the delivery should include:
ventilation unit VU01
cable of the length as ordered
sensor mounting hardware (affixed to VU01):
-(1 x) sensor mounting plate and gasket
-(4 x) M5x10 screw
torx key T25 (1 x)
VU01 mounting hardware:
-(2 x) M5x60 screw
-(2 x) M5 retaining torque nut
-(4 x) ø 5 x 10-3 m washer
spare filter (1 x)
product certificate
any other options as ordered
1.3 Options
longer cable, in multiples of 5 metres. Specify total cable length. Please consult
Hukseflux.
pack of 5 filters. Specify order number VU01F.
1.4 Quick instrument check
A quick test of the ventilation unit can be done by using a simple hand held multimeter
and a 12 VDC power supply, using the wiring diagram in chapter 5 of this manual.
1. Check the electrical resistance of the two heaters; 27 Ω each
2. Connect fan wires to a 12 VDC power supply: the fan should run
3. When running, the status of the fan can be monitored by measuring a fan status
signal (see chapter 5 for the optional status monitoring configuration instructions).

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2Instrument principle and theory
Figure 2.1 Overview of VU01 with SR20:
(1) SR20 cable
(2) SR20 connector
(3) SR20 dome
(4) VU01 cover
(5) VU01 fixation of cover
(6) VU01 levelling feet
(7) VU01 filter retainer
(8) VU01 ventilator, heaters and filter replacement system (below cover)
(9) VU01 connector
(10) VU01 cable and cable connector
Ventilation promotes thermal equilibrium between all components of radiometers, and
thereby reduces zero offsets. Dew and frost formation is prevented. Additional heating
will promote evaporation of water droplets and sublimation of snow. It should be noted
that heating in combination with pyranometers will lead to increased thermal offsets, so
heating is only recommended if necessary.
1
2
3
4
5
6
7
6
8
9
10

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3Specifications of VU01
3.1 Specifications of VU01
VU01 is a high-quality ventilation unit that may be used with pyranometer models SR20,
SR20-D2, SR22, SR25 and SR25-D1, and pyrgeometer models IR20 and IR20WS. Its
purpose is to improve the dependability of the measurement. Measurement accuracy
improves because offsets are reduced. Reliability benefits from prevention of dew and
frost formation and quick evaporation and sublimation of water and snow. For
specifications of pyranometers and pyrgeometers, please consult the SR20, SR20-D2,
SR22, SR25, SR25-D1 and IR20 manuals.
Table 3.1.1 Specifications of VU01 (continued on next page)
VU01 SPECIFICATIONS
Compatible instruments
SR20, SR20-D2, SR22, SR25, SR25-D1, IR20, IR20WS
Compliance with standards
ISO/TR 9901
BSRN operations manual
Rated operating power
7.8 W at 12 VDC (unheated)
Rated operating voltage range
10.8 to 13.2 V
Rated air flow
50 m3/hr
Rated operating temperature range
-40 to +70 oC
Fan status signal
2.5 VDC (optional use)
High = fan OK = 2.5 V
Low = fan NOT OK = ≤0.4 V
Heating
5 and 10 W at 12 VDC (optional use)
Increase of air temperature
0.5 oC at 0 W heating; 1.0 oC at 5 W heating;
1.5 oC at 10 W heating
Zero offset a SR20 ventilated
2.5 W/m2 at 0 W heating
Offset SR20 by heating
-2 W/m2 at 5 W heating
Offset SR20 by heating
-4 W/m2 at 10 W heating
Offset IR20 by heating
0 W/m2 at 5 W heating
Offset IR20 by heating
0 W/m2 at 10 W heating
Cable resistance
0.3 Ω/m (2 x 0.15 Ω/m)
Voltage drop at 7.8 W ventilation
0.2 V/m
Voltage drop at 10 W heating power
0.12 V/m
Footprint diameter
0.17 m
Fan rotation rate
5050 to 5400 1/min at 12 VDC
Standard cable length (see options)
5 m
Cable diameter
5.3 x 10-3 m
VU01 connector
M16 straight connector, male thread, 10-pole
VU01 connector type
HUMMEL AG 7.820.400.000 straight connector, male
thread, for cable 5 to 9 x 10-3 m
Cable connector
M16 straight connector, female thread, 10-pole
Cable connector type
HUMMEL AG 7.810.300.00M straight connector, female
thread, for cable 3 to 6 x 10-3 m, special version
Connector protection class
IP67 / IP69K per EN 60 529 (connected)
Cable replacement
replacement cable with cable connector can be ordered
separately from Hukseflux
IP protection class VU01
IP54

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Ø 5
140
Ø 165
124
Table 3.1.1 Specifications of VU01 (continued)
Gross weight including 5 m cable
1.55 kg
Net weight including 5 m cable
1.35 kg
Packaging
box of (330 x 250 x 220) mm
VERSIONS / OPTIONS / ACCESSORIES
Longer cable, in multiples of 5 metres
option code = total cable length; consult Hukseflux
see chapter 5.5 on installation design considerations
Pack of 5 dust filters
order code = VU01F
3.2 Dimensions of VU01
Figure 3.2.1 Dimensions of VU01 in 10-3 m.

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4Standards and recommended practices
for use
Pyranometers are classified according to the ISO 9060 standard and the WMO-No. 8
Guide. In any application the instrument should be used in accordance with the
recommended practices of ISO, IEC, WMO and / or ASTM.
Pyrgeometers are not subject to standardisation. The World Meteorological Organization
(WMO) is a specialised agency of the United Nations. It is the UN system's authoritative
voice on the state and behaviour of the earth's atmosphere and climate. WMO publishes
WMO-No. 8; Guide to Meteorological Instruments and Methods of Observation, in which
paragraph 7.4 covers "measurement of total and long-wave radiation". For ultra high
accuracy measurements, the following manual may serve as a reference: Baseline
Surface Radiation Network (BSRN) Operations Manual, Version 2.1, L. J. B. McArthur,
April 2005, WCRP-121, WMO/TD-No. 1274. The BSRN manual also includes chapters on
pyrgeometer installation and calibration.
Table 4.1 Standards with recommendations for instrument ventilation
STANDARDS FOR INSTRUMENT USE FOR SOLAR AND LONGWAVE RADIATION
ISO STANDARD
EQUIVALENT
ASTM STANDARD
WMO
ISO/TR 9901:1990
Solar energy -- Field
pyranometers -- Recommended
practice for use
ASTM G183 - 05
Standard Practice for Field
Use of Pyranometers,
Pyrheliometers and UV
Radiometers
WMO-No. 8; Guide to
Meteorological Instruments
and Methods of Observation,
chapter 7, measurement of
radiation, 7.3 measurement
of global and diffuse solar
radiation, 7.4 measurement
of total and long-wave
radiation
BSRN Operations Manual,
Version 2.1, April 2005

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5Installation of VU01
5.1 Installation of the ventilation unit
Once the VU01 cover is removed, the ventilation unit can be mounted to a flat mounting
surface using the supplied VU01 mounting hardware.
Optionally a large hole can be made by the user in the mounting surface under VU01 if
obstruction of the airflow from the sides is expected, for example by snow buildup.
The hole diameter should not exceed 120 x 10-3 m.
5.2 Installation of the sensor
Remove the pyranometer’s or pyrgeometer’s sun screen.
Attach the sensor mounting plate to the bottom of the sensor using two M5x10
screws (See Figure 5.2.1). A T25 torx key to do so is included with VU01.
Affix the sensor with the sensor mounting plate to the ventilation unit using two
M5x10 screws (See Figure 5.2.1 for placement of the gasket).
The sensor cable connector should be positioned alongside the engraved “cable”
marking on the VU01 base.
The VU01 levelling feet can be used to fine-tune the sensor levelling. Even with the
VU01 cover installed (see next page), the sensor can still be levelled since the
instrument’s bubble level is still visible below the VU01 cover.
Figure 5.2.1 VU01 base with gasket, sensor mounting plate and SR20 pyranometer: the
instrument is affixed to VU01 using four M5x10 screws.

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5.3 Installation of the VU01 cover
To install:
Connect the sensor cable connector (3) to the sensor, guiding the connector through
the designated hole in the VU01 cover
Position the cover (2) at an angle on positioning pin (5)
Close the cover using positioning pin (5) as swivel point
Affix the cover using thumbscrew (1)
Connect the VU01 cable connector to the VU01 connector (4)
To remove cover:
Loosen thumbscrew (1) by turning counterclockwise until the tapered part of the
thumbscrew is ejected from the ventilation unit base
Lift the cover, tilting around positioning pin (5)
Figure 5.3.1 Installation and removal of ventilator cover: (1) VU01 thumbscrew, (2)
VU01 cover, (3) sensor connector, (4) VU01 connector, (5) VU01 positioning pin.
Figure 5.3.2 Cutaway of VU01 showing internal components and SR20 pyranometer.
1
2
3
4
5

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5.4 Electrical connection of VU01
The cables of VU01 and Hukseflux secondary standard pyranometers and research grade
pyrgeometers have an identical M16 straight connector. Do not connect the VU01
connector to the SR20 / SR22 / SR25 / IR20 cable and do not connect the SR20 / SR22 /
SR25 / IR20 connector to the VU01 cable; both VU01 and the sensor will not function.
Cables generally act as a source of distortion, by picking up capacitive noise. We
recommend keeping the distance between VU01 and a power supply as short as possible.
For cable extension, see the next paragraph and appendix on this subject.
Table 5.4.1 The electrical connection of VU01. The heaters and fan status signal are not
necessarily used; their use is optional.
PIN
WIRE
VU01
CONNECTION
1
Brown
fan [+]
12 VDC [+]
4
Yellow
fan [−]; fan status signal [−]
common [−]
6
Blue
fan status signal [+]
2.5 VDC [+]
2
Red
heater 1 [+]
12 VDC [+]
8
Grey
heater 1 [−]
common [−]
3
Pink
heater 2 [+]
12 VDC [+]
5
Green
heater 2 [−]
common [−]
7
White
not connected
not connected
9
Black
shield
ground
Optionally the user can measure a fan status signal to monitor the status of the fan as
shown in the wiring diagram in figure 5.6.2. See paragraph 5.6 in this manual on using
the fan status signal.

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5.5 Power supply and cable length
Standard VU01 is delivered with a cable length of 5 m. Longer cable lengths, in multiples
of 5 metres, are offered by Hukseflux. Please consult Hukseflux.
In case of cable replacement or extension beyond 5 m, please note that the voltage drop
across the regular VU01 cable becomes significant and that a cable with a lower electrical
resistance must be used. Otherwise VU01 may not get a sufficient amount of power
supply. The ventilator needs a supply between 10.8 and 13.2 VDC.
Voltage drop is the part of the power supply voltage that is lost along the circuit leading
to the equipment. In this case the voltage drop is caused by the electrical resistance of
the cable. The voltage drop is proportional to the current and to the the electrical
resistance of the 2 wires in the cable leading to the ventilator; a high cable resistance
casuses a high voltage drop. VU01 power consumption is 7.8 W at a low voltage (12
VDC). The current that is needed, 0.66 A, causes a significant voltage drop.
Using a 12 VDC power supply and a cable of 5 m, the voltage drop is around 1 V and the
VU01 ventilator will effectively run on 11 VDC.
To prevent VU01 from receiving an supply voltage that is too low, the user can choose
between the following options:
1. Move the power supply closer to VU01, thereby reducing cable length;
2. Use a cable with lower electrical resistance per meter;
3. Use a combination of the above
Cable resistance and voltage drop can be calculated using the ventilator current draw:
Udrop = Ifan∙Rcable
Rcable = 2∙(Rewire∙Lcable)
Ufan = Usupply - Udrop
Table 5.5.1 Power supply variables
SYMBOL
QUANTITY
VALUE
Usupply
Supply voltage [V]
Udrop
Voltage drop over cable [V]
Ufan
Fan voltage supply [V]
10.8 to 13.2 VDC (12 V nominal)
Rcable
Cable resistance [Ω]
Rewire
Wire resistance per meter [Ω/m]
Lcable
Cable length [m]
Ifan
Fan current draw [A]
590 to 660 mA (655 mA nominal)

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The table below shows the voltage drop for several cable lengths and AWG (American
wire gauge). Different AWG wires differ in wire diameter and electrical resistance. The
table may be used to estimate the right type of wiring for installations using up to 50
metres of cable; i.e. 100 m of internal wire. Check your cable distributor for actual
resistance values. Acceptable voltage drops, when using a 12 VDC power supply, are
indicated by grey shading.
Table 5.5.2 Voltage drop for different cable lengths and AWG wires. Wires length is 2
times cable length. Resistance values are retrieved from ASTM B258-14.
AWG 26
AWG24
AWG 22
AWG 20
AWG 18
AWG 16
AWG 14
Cable
length
Udrop
Udrop
Udrop
Udrop
Udrop
Udrop
Udrop
[m]
[V]
[V]
[V]
[V]
[V]
[V]
[V]
1
0.2
0.1
0.1
0.0
0.0
0.0
0.0
5
1
0.5
0.3
0.2
0.1
0.1
0.1
10
1.1
0.7
0.4
0.3
0.2
0.1
15
1.0
0.6
0.4
0.3
0.2
20
0.9
0.5
0.3
0.2
30
0.8
0.5
0.3
40
0.7
0.4
50
0.9
0.5
Examples: For a cable length of 50 metres, the resistance of AWG16 is low enough to
deliver 11.1 V to VU01 when using a 12 VDC power supply. For a cable length of 15
metres, AWG 26 and AWG 24 cabling should not be used because the voltage drop
prohibits VU01 from receiving a sufficient amount of power.
Warning: Voltage supply to VU01 must be between 10.8 and 13.2 VDC, higher voltages
may cause damage to the fan. The voltage supplied to VU01 should be measured when
VU01 is connected.
Combinations of different cable lengths, AWG sizes and voltage supply are also possible,
but have to be calculated for each case.
Standard VU01 is delivered with a cable length of 5 m. Longer cable lengths, in multiples
of 5 metres, are offered by Hukseflux. Please consult Hukseflux.

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5.6 Using the status signal for monitoring
VU01 provides users with a fan status signal which may be used to monitor rotation of
the fan. Using the fan status signal is optional. The fan status signal is either high (OK)
or low (not OK). The VU01 status signal emits a high, continuous signal during trouble-
free operation of the fan. When the fan is running too slowly or not at all, a low signal is
provided. When opting for using the signal, please read this chapter and see paragraph
5.4 for the electrical connection of VU01.
A signal, US,high, is provided when the fan rotation rate N is above the fan rotation rate
threshold, Ng, of 1500 rotations per minute. The signal is 2.5 V. When the fan is running
too slowly or not at all, a low signal US,low is provided. The fan status signal will only
function when VU01 itself is powered.
Figure 5.6.1 A fan status signal, US,high, is provided when the fan rotation rate N is
above the fan rotation rate treshold Ng. The fan status signal emits a high, continuous
signal during trouble-free operation of the fan. When the fan is running too slowly or not
at all, a low signal US,low is provided. Using the fan status signal is optional.
Table 5.6.1 Fan status signal variables
SYMBOL
QUANTITY
VALUE
STATUS
US,high
Fan status signal high [V]
2.5 V
OK
US,low
Fan status signal low [V]
≤0.4 V
not OK
N
Fan rotation rate [1/min]
Ng
Fan rotation rate threshold [1/min]
1500 / min ± 100 /min
t2
Fan status signal start-up interval [s]
< 15 s
time [s]
time [s]
[V]
N[1/min]
U
U
N
(rotation rate)
S, high
S, low
g

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VU01 includes an internal load resistor, allowing direct use of the fan status signal. To
use the optional status signal, the user has to measure the signal between the blue (fan
status signal [+]) and yellow (fan status signal [-]) wire, as shown in Figure 5.6.2.
Figure 5.6.2 Wiring diagram required to use VU01’s fan status signal. To use the
optional status signal, the user has to measure the signal between the blue and yellow
wire. The use of the fan status signal is optional. See table 5.4.1 for the electrical
connection of VU01.

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6Maintenance and trouble shooting
6.1 Recommended maintenance
For maintenance and trouble shooting of pyranometers or pyrgeometers consult the
SR20, SR20-D2, SR22, SR25, SR25-D1 or IR20 manual.
When conducting maintenance on VU01, always power off the ventilation unit.
Powering off VU01 may be done by disconnecting the VU01 connector.
Table 6.1.1 Recommended maintenance of VU01
6.2 Life expectancy
The life expectancy of the fan itself is more than 45.000 hours under normal operating
conditions.
6.3 Trouble shooting
Table 6.3.1 Trouble shooting for VU01
PROBLEM
SOLUTION
Fan and / or heaters do not function
check wiring for correct connection of [+] and [-]
check power supply
Fan does not work
check for obstructions of fan
Fan provides little airflow
check for obstructions of airflow
replace dust filter if clogged
check wiring connections
MINIMUM RECOMMENDED VENTILATION UNIT MAINTENANCE
INTERVAL
SUBJECT
ACTION
1
1 week
check
check the operational status of the ventilator and heaters by
checking the optional fan status signal or by on-site inspection
2
1 week
cleaning
clean ventilator cover and ensure air inlet is free of
obstructions such as leaves or snow buildup
3
6 months
filter
replace dust filter, as described in the appendix

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