An aneroid barograph uses pressure-sensitive capsules, an amplifying linkage and a pen to record pressure continuously on chart paper carried by a clock-driven drum.
Aneroid Barograph Scale Reference
Relate selected full-span capsule travel, pen travel, pressure span and chart-drum period without implying a calibrated linkage.
Equation Used
- Capsule and pen travels are selected full-span magnitudes over the same pressure span.
- The ideal displacement relation is linear.
- The drum rotates uniformly through one revolution per selected period.
- Capsule force, linkage closure, errors and calibration are excluded.
Pressure span is expressed in hPa; 1 hPa equals 1 mbar.
Capsule-to-chart recording chain
Atmospheric-pressure change deflects an aneroid capsule stack. A linkage magnifies that motion and moves a pen across a pressure scale while the clock-driven drum advances the time axis.
The WMO notes that a barograph is similar to an aneroid barometer but uses a recording pen and requires attention to capsule control, friction, temperature compensation, hysteresis and calibration.
What the calculator determines
Select full-span capsule travel x, target full-span pen travel y, pressure span ΔP and drum period T. The calculator reports the ideal displacement ratio y/x, assumed capsule scale x/ΔP, chart scale y/ΔP and drum rate 360/T.
Selected full-span scale arithmetic
M = y/x. Capsule scale is x/ΔP and chart scale is y/ΔP. For a drum completing one revolution in T days, angular rate is 360°/T per day.
Selected-input arithmetic
For 0.8 mm capsule travel, 30 mm pen travel and 100 hPa span, ideal ratio is 37.5×, capsule scale 0.008 mm/hPa and chart scale 0.300 mm/hPa. A seven-day drum turns about 51.43° per day.
Model boundary
These are selected full-span ratios, not a calibrated instrument design. Capsule force, nonlinearity, effective area, temperature compensation, hysteresis, linkage geometry, friction, backlash, pen force, chart curvature, gearing accuracy and trace error are not calculated.
The animation shows a connected schematic chain but does not assert that the displayed lever lengths realize the selected amplification.
Questions
Does capsule travel come from pressure automatically?
No. It is a selected or measured full-span input.
Is the required ratio enough to design the linkage?
No. A practical linkage also requires geometry, force, travel, error and friction analysis.
Why use hPa?
One hPa is numerically equal to one mbar; modern meteorological guidance uses hPa.
Linear actuator checks for Self-registering Barometer Mechanism
An actuator-driven version of self-registering barometer mechanism should be reviewed for stroke, linkage angle, and peak force. The mechanism may feel light through most of the travel and still bind or spike in force at one position.
With leverage, force is traded against travel. A bracket change that improves force can also increase required stroke, slow the output motion, or move the actuator into a poor mounting angle.
If the application needs synchronized motion, feedback should be treated as a requirement rather than an accessory. Two open-loop actuators wired together can drift apart when friction, load, or mounting geometry differs between sides.
- Map actuator stroke to the actual output travel before choosing a model.
- Check for binding, changing leverage, and peak load near the ends of travel.
- Decide whether timed motion is acceptable or position feedback is required.
For a FIRGELLI design review, calculate the load case with the FIRGELLI actuator force calculator and plan the switching or controller arrangement with the linear actuator wiring diagram generator. If an actuator or cylinder is already installed, the linear actuator replacement finder helps keep the comparison tied to real dimensions.
References & Further Reading
- Wikipedia contributors. Barograph. Wikipedia
Building or designing a mechanism like this?
Explore the precision-engineered motion control hardware used by mechanical engineers, makers, and product designers.
