Kippzonen BSRN Scientific Solar Monitoring System Instrukcja Użytkownika Pobierz pdf (Strona 57)

Of secondary importance in the selection of the DAS is its programmability. While the minimum requirement

for the DAS is to measure a set of signals with a 0.01% accuracy at 1 Hz, the output to be archived

is the one minute mean, minimum, maximum, and the standard deviation. Thus one can store the second

data and post process the results or use the features associated with the DAS. In overall storage

requirements and operator ease, the programmable DAS is the more attractive option.

5.2 Set-up Considerations

Depending upon the location of the instruments, the accessibility of laboratory space and the overall

climatic conditions, the installation of the DAS may be near the instruments (within 5 m) or somewhat

distant inside a laboratory. The ideal site would have a completely clim ate-controlled building within

a few metres of the instruments (e.g., rooftop measurements with a laboratory below). When this does

not occur, the decision must be made as to what will provide the higher quality data; the use of a robust

data logger near the instruments or increased cable length to reach a bench model DAS.

Having a data system that functions in all environmental conditions eliminates the problems of signal

loss along cables and the potential of electrical interference. However, the design and/or operation

of a robust outdoor system usually involves some sacrifice in measurement frequency and/or data

availability and/or accuracy.

For increased quality control it is recommended that the DAS be one that has the capability of displaying

measured data (either in raw or engineering form) in near real time (e.g., within 2 minutes), preferably

graphically. The station operator should be able to examine, anytime, both the instantaneous

measurements and the data acquired during the preceding few hours or even the last day. With recent

developments in serial communications and scientific display software for PC’s, this can be easily

accomplished with both types of DAS.

Whatever the choice, internally or externally housed, the DAS must be both secure and easily accessible -

secure against inadvertent reprogramming or physical harm and accessible for easy maintenance

and changes in software or signals. It is highly recommended that a secondary external power supply

be used as insurance against loss of primary power. This may include an uninteruptable power supply

(which will also reduce the possibility of damage from power surges) for bench and computer-style

acquisition systems and a secondary battery or battery charger connected to the main battery of systems

developed to operate on DC power.

The operator must consult the manuals provided by the DAS manufacturers for the specific set-up

requirements of the system. When several different products are purchased, it is preferable that they

are bought from the same supplier as a package to alleviate the problem of attempting to determine

which one of several products is in conflict during the initial installation.

5.3 Standard Practices

(1) Each signal should be connected as a differential input to ensure the greatest measurement

accuracy.

(2) The minimum integration time for radiation signals should be one power line cycle to eliminate

powerline frequency noise.

(3) Every two years: Calibrate the ADC in an accredited standards’ laboratory. This is important

even if constant voltages and resistance are input into the system on a continuous basis (see

below). Check the associated multiplexer for changes in noise levels and settling time and

repair or replace as required.

5.4 Suggested Practices

(1) Test the pyranometer input to the data acquisition system.

(i) Measure the electrical zero. This test should be done near the location where the

pyranometer is to be placed to ensure that the cabling is free from induced signals.

Disconnect the pyranometer and replace it with a resistor of about the same value as

the pyranometer resistance. Check that the voltage reading is zero to the accuracy

specified for the data acquisition system. If not, determine whether the output is due

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