SECTION 7. MEASUREMENT PROGRAMMING EXAMPLES

This section gives some examples of Input Programming for common sensors used with the CR10. These examples detail only the connections, Input, Program Control, and Processing Instructions necessary to perform measurements and store the data in engineering units in Input Storage. Output Processing Instructions are omitted (see Section 8 for some processing and program control examples). It is left to the user to program the necessary instructions to obtain the final data in the form desired. No output to final storage will take place without additional programming.

The examples given in this section would likely be only fragments of larger programs. In general, the examples are written with the measurements made by the lowest numbered channels, the instructions at the beginning of the program table, and low number Input Storage Locations used to store the data.

It is unlikely that an application and CR10 configuration exactly duplicates that assumed in an example.

These examples are not meant to be used verbatim; sensor calibration, input channels, and input locations must be adjusted for the actual circumstances. Unless otherwise noted, all excitation channels are switched analog output.

7.1SINGLE-ENDED VOLTAGE - LI200SSILICON PYRANOMETER

The silicon pyranometer outputs a current which is dependent upon the solar radiation incident upon the sensor. The current is measured as the voltage drop across a fixed resistor. The Campbell Scientific LI200S uses a 100 ohm resistor. The calibration supplied by LI-COR, the manufacturers of the pyranometer, is given in µA/kW/m2. To convert calibration values to volts multiply the µA calibration by the resistance of the fixed resistor.

The calibration of the pyranometer used in this example is 76.9 µA/kW/m2, which when multiplied by 100 ohms equals 7.69mV/kW/m2. The multiplier used to convert the voltage reading to kW/m2 is 1/7.69mV/kW/m2 = 0.13004 kW/m2/mV.

Most LI-COR calibrations run between 60 and 90 µA/kW/m2, which correspond to calibrations of

6.0to 9.0mV/kW/m2. Above the earth's

atmosphere, the flux density through a surface normal to the solar beam is 1.36kW/m2; radiation

at the surface of the earth will be less than this. Thus, the 25mV scale provides an adequate range (9.0mV/kW/m2 x 1.36 kW/m2 < 25mV).

CONNECTIONS

The pyranometer output can be measured with a single-ended voltage measurement on channel 5. There are twice as many single- ended channels as differential channels and they are numbered accordingly: Single-ended channel 5 is the high side of differential channel

3(3H); the low side (3L) is single-ended channel

 

 

PROGRAM

01:

P1

Volt (SE)

01:

1

Rep

02:23 25 mV 60 Hz rejection Range

03:

5

IN Chan

04:1 Loc [:RAD kW/m2]

05:.13004 Mult

06:

0

Offset

FIGURE 7.1-1. Wiring Diagram for LI200S

7-1