Kintech Engineering Geovane, Руководство пользователя, Страница: 27 / 49

28
One way to maximize the accuracy of the analog voltage outputs when using cable
lengths over approx. 100m is by reducing the total resistance in the return path
that runs from pin Out (V-) to the logger, either by increasing the cable cross-
section or by wiring two cores in parallel for pin Out (V-).
Current flowing through Out (V-) is constant and around 800µA. To help you
decide whether or not the voltage drop along the analog return path is admissible
the following equation can be used as a benchmark:
𝑒𝑟𝑟𝑜𝑟 = 𝑚𝑒𝑎𝑠𝑢𝑟𝑒𝑑 𝑣𝑎𝑙𝑒 − 𝑎𝑐𝑡𝑢𝑎𝑙 𝑣𝑎𝑙𝑢𝑒
𝑒𝑟𝑟𝑜𝑟 = 𝑐𝑜𝑛𝑣𝑒𝑟𝑠𝑖𝑜𝑛 𝑓𝑎𝑐𝑡𝑜𝑟 ∙ 𝑉
𝑑𝑟𝑜𝑝
= 𝑚 ∙ (𝑅
𝑟𝑒𝑡𝑢𝑟𝑛
∙ 𝐼
𝑟𝑒𝑡𝑢𝑟𝑛
) = 𝑚 ∙ (𝜌 ∙
𝐿
𝑆
∙ 800µ𝐴)
For instance, for 92m of 0.5mm 2 cross-sectioned copper wire, the theoretical
True North offset error, given in degrees, would be:
𝑒𝑟𝑟𝑜𝑟 = 90 ∙ (0.0172 ∙
92
0.5
∙ 800µ𝐴) = +0.228°
If two cores are wired in parallel for Out (V-), the theoretical drift is reduced by
half:
𝑒𝑟𝑟𝑜𝑟 = 90 ∙ (0.0172 ∙
92
2 ∙ 0.5
∙ 800µ𝐴) = +0.114°
Remark:
At startup and until the Geovane is able to measure for the first time, the True
North offset output is set to 370º. In this way, the installer can verify that the
Geovane is operating properly even in the absence of sunlight (see section 3.4).
6.2 Frequency output
The frequency output can be configured to:
 True North offset.
The frequency output is digitally generated by the microcontroller and
subsequently conditioned by an analog push-pull output stage with 220Ω output
resistance.