IMPORTANT MODIFICATION TO THE DrDAQ BAROGRAPH
Additional work on the DrDAQ Barograph showed that the unwanted pressure cell output voltage variation did not agree with the calculated oil density variation with temperature: in fact output voltage change was notably greater than that theoretically caused by density variation.
Further research found that the additional temp. variation was caused by pipe C which plugs Port 2. An increase in ambient temperature causes the residual air inside the pipe to expand, parasitically reducing cell output voltage, because of increased pressure at differential Port 2 and vice-versa. This mechanism has nothing to do with oil density variation.
The simple modification is to remove pipe C and plug Port 2 directly with conglomerating tape. This modification is shown in the uploaded drawing. Future posts will show non only the new temp. compensation expression, but a very important simplification and improvement of the barograph.