Kipp&Zonen SMP3 Pyranometers - Manual (Page 23)

.
Please follow the instructions in this section carefully for the mechanical and electrical installation of the SMP series pyranometers.
Do not turn on power to the instrument until instructed to do so.
Note Do not connect the instrument to a computer until instructed to do so.
Note Do not turn on power to the operating computer until instructed to do so.
2.1 Included with the product
Check the contents of the shipment for completeness (see below) and note whether any damage has occurred during transport.
If there is damage, a claim should be filed with the carrier immediately. In the case of damage and/or the contents are incom-
plete, contact your local Kipp & Zonen representative or e-mail the Kipp & Zonen customer and product support department at:
[email protected]
Although all SMP radiometers are weather-proof and suitable for use in harsh environmental conditions, they have some
delicate mechanical parts. Please keep the original packaging for safe transport of the radiometer to the measurement site, or
for use when returning the radiometer for calibration.
The following items are included with SMP pyranometers:
Smart Pyranometer
Sun screen
Cable, pre-wired with 8-pins connector or connector only for customer cable
Calibration certificate
Instruction sheet
Pyranometer fixing kit SMP3; 2 each of stainless steel M5 x 30, M5 x 40 and M5 x 50 mm screws, nut, flat washer
Pyranometer fixing kit SMP10/SMP11; 2 each of stainless steel M5 x 80 mm screw, nut, flat washer, nylon insulation ring
2 Dessicant bags (SMP11 only)
CD with product documentation and software
.
Below is a brief description of the accessories available for SMP series pyranometers. Detailed information can be found on our
website, where the brochures and manuals for these accessories can be viewed and downloaded.
3.1 Diffuse radiation measurement
For measuring diffuse radiation a shading device is required. Kipp & Zonen can offer several options for SMP pyranometers:
Shadow ring CM 121B for a SMP3 or an unventilated SMP10 or SMP11
Shadow ring CM 121C for a ventilated SMP10 or SMP11
This shadow ring needs to be adjusted manually every 3-5 days and corrections made for the sky obscuration by the ring.
An automated and more accurate way to measure diffuse radiation is to use an automatic sun tracker fitted with a shading
mechanism:
2AP sun tracker + shading ball assembly
SOLYS 2 sun tracker + shading ball assembly
3.2 Ventilation
To further improve measurement accuracy of the SMP10 and SMP11 pyranometer the CVF4 ventilation unit can be used. CVF4
has a tacho output to monitor the fan speed and 5 or 10 Watt heater. The advantages of a CVF4 are:
Lower thermal offsets
No precipitation or condensation on the dome
Less dirt on the dome
Frost, snow or ice can be melted
Less frequent cleaning required
3.3 Mountings
For mounting pyranometers the following plates and brackets are available:
Mounting rod for SMP3
CMF 1 mounting fixture with rod for mounting one or two unventilated SMP10’s or SMP11’s
CMF4 mounting plate with rod for mounting one or two ventilated SMP10’s or SMP11’s
CMB 1 mounting bracket to fix and adjust a mounting rod to a mast, pole or wall
Adjustable tilt mounting kit allows tilting of a SMP pyranometer (e.g. in the same plane as a PV panel), It has a
clear scale for setting the desired angle.
3.4 Glare screen kit
When a SMP10 or SMP11 pyranometer is mounted looking downwards, to measure reflected radiation, it should be fitted with
the glare screen kit. The screen blocks radiation coming from the 5 ° below the horizon of the pyranometer, to prevent direct
illumination of the domes by the sun at sunrise and sunset.
3.5 Cables
As standard a 10 m long cable with a pre-wired waterproof connector plug is supplied. Optional longer cables are available, or
a loose connector only for you to fit to your own cable.
25 m cable with connector
50 m cable with connector
Loose connector without cable
3. Accessories
2.2 Tools required
The tools required to fit an SMP series pyranometer to a support are a 4 mm (M5 socket head screw) Allen key and a 8 mm (M5
nut) wrench / spanner. Normally, the drying cartridge for the SMP11 should be hand-tight, but a 16 mm or 5/8” open-ended
wrench / spanner can be used to loosen it.
2.3 Location and support
The instruction sheets contain all the outline information necessary for the correct installation of the pyranometers. Further
detail for specific types of installation and application are given later in this section.
Check the condition of the desiccant in the SMP11 and replace before installation, if necessary; for example after a long storage
period. This is not required for SMP3. The SMP10 internal desiccant is operational 10 years after the last calibration date as
mentioned on the instrument label and calibration certificate.
When using the digital output it might be convenient to set the Modbus® address prior to visiting the site, otherwise a computer
and RS-485 / USB converter may be required during installation.
2.4 Installation for measurement of horizontal global irradiance
The following steps must be carefully taken for optimal performance of the instrument.
2.4.1 Location
Ideally, the site for the radiometer should be free from any obstructions to the hemispherical view from the plane of the detector.
If this is not possible, the site should be chosen in such a way that any obstruction over the azimuth range between earliest
sunrise and latest sunset should have an elevation not exceeding 5 ° (the apparent sun diameter is 0.5 °).
This is important for an accurate measurement of the direct solar radiation component. The diffuse solar radiation is less
influenced by obstructions near the horizon. For instance, an obstruction with an elevation of 5° over the whole azimuth range
of 360 ° decreases the downward diffuse solar radiation by only 0.8 %.
It is evident that the radiometer should be located in such a way that a shadow will not be cast upon it at any time (for example
by masts or ventilation ducts). Note that hot exhaust gas (> 100 °C) will produce some radiation in the spectral range of the
radiometer and cause an offset in the measurements. The radiometer should be distant from light-coloured walls or other
objects likely to reflect sunlight onto it, or emitting short-wave radiation.
The radiometer should be readily accessible for cleaning the outer dome, checking that it is level and inspecting the desiccant.
.
2.4.2 Mounting
The SMP pyranometer is provided with two holes for 5 mm bolts. Two nylon insulation rings and two each of stainless steel bolts,
washers and nuts are provided in the fixing kit. The pyranometer should first be secured lightly with the bolts to a solid and
stable mounting stand or platform as shown below. The nylon insulators are important to prevent corrosion between the screws
and the pyranometer housing.
The mounting stand temperature may vary over a wider range than the air temperature. Temperature fluctuations of the
pyranometer body can produce offset signals, therefore it is recommended to isolate the pyranometer thermally from the
mounting stand by placing it on its three feet. Ensure that there is a good electrical contact with the ground to conduct away
currents in the cable shield induced by lightning.
Note After recalibration and/or reinstallation ensure that the nylon insulators are refitted.
2.4.3 Orientation
In principle no special orientation of the instrument is required, although the World Meteorological Organisation (WMO) recommends
that the signal lead (connector) is pointed towards the nearest pole, to minimise heating of the electrical connections. This is also
where any mounting pole, or other support, should be located in order that shadows do not fall on the instrument.
2.4.4 Levelling
Accurate measurement of the global radiation requires proper levelling of the detector surface. Level the instrument by turning
the two adjustable feet to bring the bubble of the spirit level centrally within the marked ring. For easy levelling, first use the
screw nearest to the spirit level.
Note It is ideal that the bubble should be completely within the marked ring. However, in fact, the pyranometer is level
within the specified accuracy when the bubble is at least half within the ring.
2.4.5 Securing
Secure the pyranometer tightly with the two stainless steel bolts. Use the two nylon insulators to avoid contact between the
aluminium body and the steel screws. Ensure that the pyranometer maintains the correct levelled position when it is tightened.
.
2.4.6 Fitting the connector and cable
Locate the plug correctly in the radiometer socket, it only fits one way, and push it in. Screw the plug locking ring hand-tight.
Over-tightening may damage the waterproof seal. Secure the cable so that it cannot blow in the wind or cause a shadow on the
instrument.
Note The cable should be arranged with a curve below the instrument so that water drips off, rather than running along
the cable up to the connector.
2.4.7 Fitting the sun shield
Finally, clip on the sun shield to prevent excessive heating of the radiometer body. The bubble level is visible through the top
of the sun shield for routine checks and the shield ‘tail’ helps to protect the connector.
2.5 Installation for measurement of tilted global irradiance
When a pyranometer is mounted on a large flat tilted surface the temperature of this surface can rise considerably (more than
10 °C) above air temperature. It is advised to pre-adjust the levelling feet on a horizontal surface for easy mounting of the
instrument parallel to the inclined surface. It improves the measurement accuracy when the body is thermally isolated by its
feet from the surface. This promotes thermal equilibrium between the dome(s) and the housing and decreases zero offsets.
For accurately and securely fixing a pyranometer at an angle to a surface an adjustable tilt mounting kit is available. See Accessories
in chapter 3.
2.6 Installation for measurement of reflected global irradiance
In the inverted position the pyranometer measures reflected global radiation. The
height above the surface (H) depends upon its roughness. The WMO recommends a
height of 1 m to 2 m above a uniform surface covered by short grass.
The mounting device should not interfere significantly with the field of view of the
instrument. The mounting plate above the pyranometer prevents excessive heating of
the housing by downwards solar radiation and. The glare screen has an angle of 5 °
and is fitted to the pyranometer to prevent direct illumination of the domes by the sun
at sunrise and sunset. It is available as an accessory kit for the SMP10 and SMP11.
Thermal offset signals generated in the pyranometer are 5 times more significant
in the measurement of reflected radiation due to the lower irradiance level.
The mast shown intercepts a fraction D/2πS. of the radiation coming from the
ground. In the most unfavourable situation (sun at zenith) the pyranometer
shadow decreases the signal by a factor R2/H2.
As a guide, a black shadow below the pyranometer with a radius of 0.1 x H decreases the signal by 1%, and 99 % of the signal
will originate from an area with a radius of 10 x H.
2.7 Installation for measurement of albedo
An albedometer consists of two identical pyranometers that measure the
incoming global solar radiation and the radiation reflected from the surface
below. Albedo is the ratio of the two irradiances, and varies from 0 (dark)
to 1 (bright).
Two SMP3’s can be mounted back to back with the standard fixing kit, and the
accessory mounting rod screwed into one of them, to make an albedometer.
For two SMP10’s or two SMP11’s a mounting plate is required. The CMF 1
mounting plate is used for unventilated SMP10’s or SMP11’s and the CMF4 for
ventilated instruments. There is no ventilation unit for the SMP3.
The requirements for installation of the upper pyranometer are the same as
for horizontal global irradiance. The requirements for installation of the
lower pyranometer and mast are the same as for reflected global irradiance.
2.8 Installation for measurement of horizontal diffuse irradiance
For measuring the diffuse radiation from the sky, the direct solar radiation
must be blocked from the pyranometer dome(s).
A static shadow ring can be used to intercept the direct solar radiation. This
requires frequent manual adjustment as the sun’s arc in the sky changes. At
times the shadow ring also intercepts a significant proportion of the diffuse
sky radiation. Therefore, post-processing of the recorded data is necessary to
correct for this.
Kipp & Zonen produces a universal shadow ring, model CM 121, which is
suitable for use at all latitudes.
The alternative to a shadow ring is to use a two-axis automatic sun tracker,
such as one of the models from Kipp & Zonen. The sun tracker uses location
and time information to calculate the position of the sun and point at it
accurately under all weather conditions.
The sun tracker can be fitted with a small disk or sphere mounted on an
articulated shading assembly. The shadow of the disk or sphere is adjusted to
cover the pyranometer dome(s) completely and it will then be shaded correct-
ly throughout the year without adjustment.
2.9 Electrical connections
As standard SMP pyranometers are supplied with a waterproof connector pre-wired to 10 m of high quality yellow cable with 8
wires and a shield covered with a black sleeve. Longer cables are available as options. The colour code of the wires and the
connector pin numbers are shown below and on the instruction sheet.
Special attention is needed to prevent power or ground loops when connecting the SMP to multiple readout devices.
Connecting the RS-485 to a grounded circuit and the analogue output to a floating circuit can cause unacceptable
ground loops. This may cause differential voltages outside the SMP specifications and will damage the unit. We
recommend using either the analogue or the digital output but not both. The maximum differential between either
of the Modbus® RS-485 lines (yellow and grey) and the power ground / RS-485 common line (black) is 70 VDC.
First connect all wires before plugging into the radiometer
The shield of the cable is connected to the aluminium radiometer housing through the connector body. Preferably,
secure the radiometer with its levelling screws on a metal support with a good connection to ground (e.g. by using
a lightning conductor) and do not connect the cable shield at the readout end.
If there is no good ground connection at the pyranometer, the shield at the cable end should be connected to ground
at the readout equipment. Lightning can induce high voltages in the shield but these will be led off at the pyranometer
or readout equipment.
Note Long cables may be used, but the cable resistance must be smaller than 0.1 % of the impedance of the readout
equipment for the analogue outputs and may affect the baud rate of the RS-485 digital connection.
2.9.1 Power connection
The minimum power supply voltage for SMP pyranometers is 5 VDC. However, for optimal performance it is advised to use
12 VDC, especially when long cables are used. 5-volt power can only be used in combination with a short cable, maximum 10 m.
It is advised to protect the output of the power supply with a fast blowing fuse of maximum 250 mA rating.
Typical power consumption SMPX-V for maximum output (1 V)
5 VDC 50 mW (approx. 10.0 mA)
12 VDC 55 mW (approx. 4.5 mA)
24 VDC 60 mW (approx. 2.5 mA)
.
Maximum power consumption 65 mW at the highest input voltage.
Maximum input current 12.5 mA at the lowest input voltage.
Maximum inrush current 200 mA.
Typical power consumption SMPX-A for max output (20 mA)
5 VDC 77 mW (approx. 28 mA with 100 Ω load resistor)
12 VDC 83 mW (approx. 24 mA with 100 Ω load resistor)
24 VDC 100 mW (approx. 6 mA with 100 Ω load resistor)
The above mW values represent the dissipation within the SMPX-A. For the total power the energy in the load resistor has to
be added.
For supply voltages below 12 Volts or above 20 Volts it is advised to use a load resistor of less than 500 Ω to keep the power
consumption as low as possible.
2.9.2 Data connection
Connection to a Personal Computer by Universal Serial Bus (USB)
The connection depends on the use of a RS-485 to USB converter.
The converter must have galvanic isolation between the inputs and outputs to prevent possible damage to the SMP
digital interface. This is particularly an issue with portable computers (laptops, etc.) in which the power supplies
can generate large voltage spikes.
A suitable converter is the model USOPTL4 from B & B Electronics. One end has the USB connector to the PC the other end has
a connector with screw terminals for the instrument wires. This RS-485 converter is powered from the USB interface, so no
additional power adaptor is necessary.
*Note Switches on the converter should be set for RS-485, 2-wire operation and Echo off.
.
*Note Switches on the converter should be set for RS-485, 2-wire operation and Echo off.
Connection to a RS-485 Network
The digital interface can be connected to a 2-wire RS-485 network as shown below.
The slaves and master may be a SMP pyranometer or other devices. If a SMP pyranometer is the last device on the network a
line terminator (LT), consisting of a 120 Ω or 150 Ω resistor, must be connected between terminals A/A
' /- and B/B ' /+. Never
place this line termination on the derivation cable. It is also required to install the pull up and pull down resistors as shown.
The value of these resistors must be between 650 Ω and 850 Ω.
2.9.3 Analogue voltage output
The SMP3-V, SMP10-V and SMP11-V (voltage output versions) have been factory set such that an output of 0 Volts represents
-200 W/m² (this will never be reached in practice), and the full-scale output of 1 Volt represents 2000 W/m².
The voltage output range in W/m² can be changed by the user with the supplied PC software. The maximum recommended
irradiance for the SMP3 is 2000 W/m² and for the SMP10 and SMP11 is 4000 W/m².
.
The measurement range must start from a negative value in order to show (small) negative readings, for example night-time
offsets, because the analogue output itself cannot go negative. For the default setting of 0 to 1 Volt representing -200 to 2000
W/m² the range is actually 2200 W/m² with a zero offset of 200 W/m².
The irradiance value ( E
solar
) for the default setting can be simply calculated as shown below.
E
solar
= Solar radiation [W/m²]
V = Output of radiometer [Volt]
If the pyranometer is used in atmospheric conditions it is advised to keep the range as factory set.
2.9.4 Analogue current output
The SMP3-A, SMP10-A and SMP11-A (current output versions) have been factory set such that an output of 4 mA represents
0 W/m² and the full-scale output of 20 mA represents 1600 W/m².
The current output range in W/m² can be changed by the user with the supplied PC software. The maximum recommended
irradiance for the SMP3 is 2000 W/m² and for the SMP10 and SMP11 is 4000 W/m².
Negative inputs will make the output go below 4 mA and no zero offset is needed.
For the default setting of 4 to 20 mA representing 0 to 1600 W/m², each mA represents 100 W/m².
The irradiance value ( E
solar
) for the default setting can be simply calculated as shown below.
E
solar
= Solar radiation [W/m²]
mA = Output of radiometer [mA]
2.9.5 Recommended cable types
Where cables need to be extended, or the customer prefers to provide their own cables, they should be suitable for outdoor used
and UV resistant.
Recommended types
RS-485 Ethernet CAT 5 shielded twisted pair (STP)
0 to 1 V Shielded 2-core signal cable
4 to 20 mA Shielded twisted pair control cable
23