Solarnet Network-Instrumentation

Field Instruments

SOLARNET Environmental Data Network

The radiometer sensor head unit is a weatherproof housing with cosine-corrected diffuser for light sampling, a filter wheel with 18 2nm-nominal band pass interference filters mounted in the periphery, a collimator, and a solar blind R-1657 photomultiplier tube (PMT). The PMT housing is temperature regulated with a thermostated thermoelectric system. The filter wheel turns at 15 RPM and has 2nm half-power-band-width light filters with nominal center wavelengths from 290nm to 324nm. The PMT current output (which is proportional to the radiation intensity through each filter) is converted to a voltage and passed to a precision 20 bit A/D converter.

Operation of the sensor head is under the control of an on-board microcontroller. Data from all light filter channels, and the two dark readings are averaged for one minute intervals, stored along with internal temperature and control information, then transmitted over RS-422 twisted pair wires to the data acquisition and control unit. All of the components within the sensor head unit are environmentally housed for extended year-around field operation. All components of the sensor head, except the PMT, are designed to operate without significant temperature effects over a -25o to +70o C temperature range. A desiccant canister filled with indicating silica gel maintains low humidity inside the sensor head. A viewing port in the canister allows the operator to determine when to replace the silica gel.

The second unit is the external power supply for the sensor head system. This power supply provides electrical power both to the head electronics and to the thermoelectric PMT temperature regulator. This unit is contained in a weatherproof housing.

The third unit, the data acquisition/control unit, consists of an MS-DOS PC with a hard drive and a 3.5 inch floppy disk drive. Data would routinely be downloaded from the hard drive to the removable floppy, or transmitted via modem to the data management facility.

A. Set up radiometer head (SR18). The set-up of solar radiation monitoring devices is a subject beyond the scope of this manual. Most importantly, the operating location should have as unobstructed a view of the sky as possible from horizon to horizon.
Refer to Instrument Case drawing in the appendix of this manual for dimensions of the instrument case.
The radiometer should be mounted on a solid mounting stand to be provided by the user.

1. Level the case before securing to mounting stand. Use the circular bubble level included with the instrument. Place the bubble level on the top face of the SR18 case. If the SR18 is not level, add shims under the case and/or the mounting brackets to level.

2. Screw the SR18 down to mounting stand with one screw through each angle mounting bracket on the side of the case, and recheck the instrument level.

B. Set up external power supply. This power supply is designed to be mounted with its cooling fins positioned vertically to increase convection cooling. The power supply has two nearly universal mounting brackets. These brackets can be used to mount the supply to any vertical surface or vertical shaft or pipe.

D. Install cabling. Refer to SR18 Interconnection Diagram, and Instrument Case and External Power Supply drawings in the Appendix of this document. Note and follow the color coding of the cable connectors as shown on interconnection diagram.

1. Install cables from external power supply to SR18.
a. Install W-1002 cable from external power supply to SR18 main case.
b. Install W-1003 cable from external power supply to SR18 heating/cooling module.

At the data acquisition end of the serial data cable is a converter module with a female DE-9 connector. This connector connects serial RS-232 signals to the data acquisition system. The protocol of the signal is 9600 baud, 8 data bits, NO parity, 1 stop bit.

E. Turn-on procedure. When 120 VAC power is applied to the external power supply and the two cables (W-1002 and W-1003) are connected from the supply to the SR18, the radiometer will begin to operate and collect data in its normal scan mode. In this mode, data will be sent from the SR18 over the communications cable (W-1004) every minute. The SR18 contains a battery-backed clock which has been set during manufacture so that the operator need now do nothing more to begin collecting data.

After the SR18 system has been installed, leveled, cabled and powered (see II. Installation Instructions) the radiometer system is ready to begin collecting data. In fact, as soon as the SR18 is cabled and powered, it will begin to collect data, and transmit that data over its communications cable. See section V. Data Stream Description for information on the format of the data and on how much data is transmitted from the radiometer. When the SR18 is first powered, its internal operating program begins running. This program first undertakes initialization and checking functions, and then waits for the start of a minute to begin data collection. Because of these start-up functions and the wait period, a period of up to three minutes may pass before the SR18 sends any data down its communication cable.

See section IV. Normal Maintenance Operations for daily and weekly checks and maintenance operations.

Data Acquisition. The SERC SR18 is designed for flexibility in data acquisition, which will allow a variety of data acquisition schemes to be used. There are several standard schemes currently in use. See the Appendix section for a description of the SERC data acquisition program.

SERC uses an acquisition program that captures data and allows the option of writing that data to a file on the PC.

For every minute the SR18 is in standard operating mode it transmits three lines of data. The first line consists of the instrument ID, and current date and time. The time indicates the time at the end of the minute which was just recorded - the minute for which the following data refers. The third line consists of diagnostic information. The second line contains twenty channels of light data. Each channel includes a channel ID indicator character (A through T) a sign character (+ or -) and a seven digit (plus decimal) voltage value. That voltage is the mean of all the scans (normally 14) made during that minute for that channel. That voltage is proportional to the irradiance in that channels filter pass band, and can be reduced to energy values (Joules per square meter per nanometer per minute) by multiplying the voltage by that channels calibration constant (see appendix).

The SR18 includes its own battery-backed clock which should not require setting in the field. There is a provision to set the clock, and to do several other diagnostic and function setting tasks. This function is called Command Mode, and is accessible to the operator by sending the SR18 a Control-A code twice up the communications line which is operating in full duplex mode. This can be done using XTALK. Call up XTALK.EXE, set the operating parameters by the NEWRAD file. Send the Control-A code twice. After receipt of the double Ctrl-A command the SR18 will wait until the end of the current minute, and then enter Command Mode. When the SR18 enters Command Mode it will send a list of its current settings down the communications line.

Sleep Time is the time that the SR18 will stop taking data each day and Wake Time is the time that the SR18 will begin taking data each day. The date and time shown are the current SR18 values. This feature allows the SR18 system to avoid collecting data during night periods. To reset the sleep or wake times press Ctrl-I or Ctrl-J respectively while in Command Mode.

Diagnostics Mode causes the SR18 to send the value for each channel for each scan down the communications line, along with the date and time of that scan.

During normal data collection the SR18 may also send a diagnostic message: WATCHDOG ALERT.

This message means that there was an operating problem in the current minute of data collection. After the SR18 sends this message, it will attempt to begin data collection and transmission in a normal manner again. If several WATCHDOG ALERT messages occur in a row (they can occur as frequently as every two seconds or up to three minutes apart), the operator should turn off the 120VAC power to the SR18, leave the power off for at least 30 seconds, and then turn on the power again. If WATCHDOG ALERT messages again occur, the SR18 will require non-field maintenance.

A. Observe for normal operation
1. Instrument should be checked at least twice each day for normal operation - early in the morning and late in the afternoon to cover as wide a time span as possible. Items to check:
a. Is data being collected normally in standard data format (see Section V. Data Stream Description)?
b. Are date and time correct in the data stream?
c. Are there 014 data sets per minute?
d. Is the STATUS: indicator 0?
e. Is the TEMP: between 0 and 60?
2. If any abnormalities are noted in the operation of the radiometer, contact the service depot. There are no field serviceable components inside the radiometer. The instrument must be returned to the service center for depot level maintenance.

B. Clean diffuser
1. Diffuser (light entrance port) should be cleaned with clear water, and wiped dry with a soft cloth at least once a week. In below freezing weather, alcohol should be used in place of water.

C. Check desiccant for dark blue color. If desiccant is depleted, as indicated by a pale blue, pink or white color it should be changed.

D. Procedure to change desiccant.
1. There are no field serviceable components inside the radiometer. Therefore the case should never be opened in the field.
2. Unscrew desiccant holder and remove from end plate.
3. Locate 0.050" socket head set screw(s) in threaded area of desiccant holder. Some desiccant holders have two set screws.
4. Hold canister with wire basket down and the viewing window up to prevent spilling of desiccant.
5. Loosen the set screw(s) that you located in step 4.
6. Gently twist basket from main (window) section of holder.
7. Discard old desiccant, or reserve for renewal. Desiccant can be renewed by heating in an oven until the dark blue color reappears.
8. Blow off any desiccant dust from both sections of the holder away from the instrument with dry air.
9. Fill the desiccant basket to the brim with fresh indicating desiccant.
10. Twist together the two sections of the holder until they mate against the stop, tighten the set screw(s).
11. Reassemble the desiccant holder to the case end plate and screw into place hand tight.

Data from SERC 18 Channel Radiometer
Each minute of data from the radiometer (using version 48 PROM software) is 280 bytes. This is an example of that one minute's data format (where <CR/LF> refers to a carriage return and line feed character pair):

UN DATE: 170896 TIME: 121701<CR/LF>
A+00.12576B+00.14404C+00.11544D+00.10206E+00.09530F+00.07946
G+00.05314H+00.06424I+00.03908J+00.00046K+00.04562L+00.03476
M+00.01582N+00.01356O+00.01418P+00.01446Q+00.01594R+00.01806
S+00.01696T+00.00042<CR/LF>
DATA SETS: 014 STATUS: 0 TEMP: +39.57 FSC: 000<CR/LF>

Including CR/LF characters: Total: 280 bytes per minute
-ID line is 30 bytes = 16,800 bytes per hour
-data line is 202 bytes = 302,400 bytes for an 18 hour day
-Status line is 48 bytes

A 290nm
B 292nm
C 294nm
D 296nm
E 298nm
F 300nm
G 302nm
H 304nm
I 306nm
J Dark Zero #1
K 308nm
L 310nm
M 312nm
N 314nm
O 316nm
P 318nm
Q 320nm
R 324nm
S 330nm
T Dark Zero #2

Enter Command Mode: Ctrl-A (twice)
Set time and date: Ctrl-B
Read Temperature: Ctrl-E
Enter Diagnostics Mode: Ctrl-F
Return to Command Mode
from Diagnostics Mode Ctrl-A (twice)
Exit from Command Mode
to Normal Operation Mode: Ctrl-G

Perform a single conversion: Ctrl-H
Set the hour for Sleep Mode (0-23): Ctrl-I
Set the hour for waking (0-23): Ctrl-J