14 December 2011

Amplified Sensors

To help satisfy the needs of some of our customers, we offer an amplified version of our pyranometer and quantum sensors. This allows for easy integration into existing systems that are not designed for millivolt signals. There are two options: 2.5V and 5V. Where the number listed is the maximum output at the maximum light for which the sensor is calibrated it is also the minimum input voltage required to power the sensor. For example: the SP-215 has an output of 4.4V when the solar radiation is at its maximum of 1100 W/m2. This allows for some head room if the light level is higher due to reflected radiation. If the voltage supplied was only 4V the maximum output would be 4V which means that the sensor would output the same for any light level over 1000 W/m2. This is something to watch for if you are supplying the voltage with batteries.

These sensors have been designed to have all the circuitry inside the head, the same as our non-amplified sensors. This means they are rugged and there is no worry about water damage to the circuit board. The circuitry is a basic non-inverting configuration of an operational amplifier (op-amp). The op-amp has been specifically chosen to have a low voltage offset and be physically small enough to fit inside of our current sensor body head. The op-amp has a max voltage specified at 5V which is why the maximum output of our amplified sensors is 5V. Included in the circuitry is a Zener diode that will short to ground if a voltage higher than 6V is applied. This keeps the main circuitry from getting destroyed if the sensor is wired incorrectly.

These voltage ranges can still be limiting for some of our customers, which is why we are working on a 4-20mA output for our sensors that we will release early next year. This circuit will have an input voltage range of 5-36V, and will significantly surpass the voltage limits of our amplified sensor.

Skif Smith
Electrical Engineering

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