Pyranometer to Current Converter

Wichit Sirichote,

This converter enables long cable wiring for pyranometer. Operated with +3V Lithium battery.

Build a micropower circuit that converts low level DC signal from pyranometer to DC current for long cable metering. The circuit was built with TLV2451, rail-to-rail input/output opamp made by TI.

Figure 1: The converter board installed under solar cell array.

The hardware block diagram is shown in Fig. 2. The pyranometer has the output 5uV/W/m^2. The first amplifier is noninverting DC amplifier having DC gain of 200. For 1000W/m^2, the output will be 1V full scale. The second opamp circuit is voltage-to-current source. The output will be 0-20mA for 0-1V input. We can have long cable for current mode transmission to the meter.

Figure 2: Hardware block diagram.

Hardware Schematic

The complete hardware schematic is shown in Fig 3. R2 and C1 forms low pass filter for averaging DC signal to the noninverting input. U1 is noninverting amplifier with DC gain 200, (1+R4/R3). U2, Q1 and R1 forms the voltage-to-current converter. The noninverting input is 1V full scale. The output of U2 drives Q1 to provide 20mA flow through external load to the R1. The circuit draws less than 60uA with +3V Lithium battery. However for high irradiance of sun light, it will draw about 100uA.

Figure 3: Hardware schematic.


Figure 4: Pyranometer.

Figure 5: Modified 20mA DC meter providing 0-1000W/m^2 reading.



I have received TLV2451 chips by TI sample distribution for educational. I got the sample within a week, sending from USA to Thailand.


Schematic schematic.pdf
TLV2451 datasheet slos218b.pdf

5 Aug 2006

recovered 17 December 2015