Example of time-series data from a subset of the chamber variables, collected after applying an impulse to load_in, the control signal of the intake fan. See the variables table for a description of these variables.
Right click to download the image (available under a CC BY-NC 4.0 non-commercial license).
| Name | Description | Documentation |
|---|---|---|
full | Full configuration with all variables. |
Right click to download the image (available under a CC BY-NC 4.0 non-commercial license).
Left: steady-state measurements of the calibrated fan current (current_in) for different values of the load load_in. Center: steady-state measurements of the fan speed (rpm_in) for different values of load_in. Due to their intended application, unless completely powered off (i.e., load_in/out = 0) the fans never operate below a certain speed, corresponding to a minimum load of 0.1 (shown by the gray line). Right: time-series data after a step increase in load_in, showing a lagged effect on fan speed (rpm_in) and current (current_in).
By setting a fan load to zero (e.g., load_out ← 0 at t=125), the fan is completely powered off and will decelerate until it stops rotating. It will no longer produce a tachometer signal, and the resulting speed measurement will be the last measured speed (see rpm_out above for 125 < t < 200). When powered up again (t=200) the fan draws full power for an instant, accelerating before returning to the level specified by the load.
Calibrated fan currents (current_in/out, top) under step changes to the fan loads (load_in/out, bottom). Because both fans share the same power supply, when a fan is operating close to its maximum load, its drawn current is affected by large changes to the load of the other fan, e.g., at t=200,300.
Measurements of fan speed (rpm_in) for different resolutions of the underlying tachometer (res_rpm_in), for increasing values of the fan load load_in. The quantization error is larger for higher speeds, when tachometer pulses occur at shorter intervals. The results for rpm_out are the same and not shown.
Left: effect on the fan speed of changing the hatch position (bottom) under constant fan loads (top and middle plot). Right: effect of applying a short impulse to load_in on the fan speeds rpm_in/out for different hatch positions. The coupling between between the fan speeds decreases as the hatch is opened. The hatch is closed at 0º, and fully open at ±45º.
Position of the hatch (hatch_angle) along a trajectory (dotted black line) defined by the input hatch that sets the desired hatch position. We show trajectories for the default motor parameters (top left) and different values of the motor parameters mot_steps/max/enabled. Lower motor resolutions (mot_steps) result in a coarser hatch placement and potential accumulation of errors. Lowering the current delivered to the motor (mot_max), or powering it off completely (mot_enabled = 0) cause the motor to miss steps, creating a mismatch between the set position (hatch) and the actual position of the hatch (hatch_angle).
Left: change in the tunnel pressures after applying an impulse to load_in (gray dashed line), causing a change in the speed of the intake fan (light gray), and creating a pressure wave inside the chamber. The hatch is kept closed (hatch=0), and the exhaust fan is held at a constant load of load_out=0.1. Center: change in the tunnel pressures after applying an impulse to load_out (gray dashed line), causing the exhaust fan to accelerate and decelerate (light gray). As before, the hatch and exhaust fan load are kept contant (hatch=0, load_in=0.1). Right: change on the tunnel pressures by opening and closing the hatch; the fans are kept at a constant load of load_in=1 and load_out=0.1.
Effect of the barometer oversampling rate (osr_pressure_upwind/downwind/ambient/intake) on the resulting measurement (pressure_upwind/downwind/ambient/intake). For all barometers, the oversampling rate is increased at t=200,400, 800, while keeping all other chamber inputs and sensor parameters constant.
Effect of the sensor parameters offset/sps/res_current_in (resp. left, center, right) on the calibrated (current_in) and uncalibrated (current_in_raw) of the intake fan (top and bottom row, respectively). The behaviour for current_out and current_mot is the same and not shown. The calibrated measurements (in Amps) largely compensate for changes in the reference voltage (offset_, left) and sensor resolution (res_, right), unless sensor saturation occurs. For example, in the right plot, the resolution (res_current_in = 2) is increased to the point where the measurements fall outside of the sensor range. Both calibrated and uncalibrated measurements are affected by changes in the oversampling rate (sps_), which affects their signal-to-noise ratio (i.e., variance, precision).
Effect of the sensor parameters offset/sps/res_mic (resp. left, center, right) on the calibrated (mic) and uncalibrated (mic_raw) measurements from the tunnel microphone (top and bottom row, respectively). The calibrated measurements (in Volts) largely compensate for changes in the reference voltage (offset_mic, left) and sensor resolution (res_mic, right), unless sensor saturation occurs. For example, in the right plot, at the smallest measurement range (res_mic = 6) some measurements fall outside of the sensor range. Saturation can be achieved with lower values of res_mic by shifting the reference voltage of the sensor through offset_mic. Both calibrated and uncalibrated measurements are affected by changes in the oversampling rate (sps_mic), which affects their signal-to-noise ratio (i.e., variance, precision).
Left: time-series data of the microphone output mic (top) collected under varying inputs (bottom) to the fan loads load_in/out and the hatch position hatch. All three inputs affect the microphone measurements. Right: marginal distribution of the microphone output mic for the colored regions on the left plot. The hatch modulates the amount of air that flows through the tunnel exhaust and over the microphone, having a slight effect on the distribution of its measurements. The effect depends on the fan loads, e.g., opening the hatch (hatch=45) decreases the airflow over the microphone when load_in=1, load_out=0.01 (top), but increases it when load_in=0.01, load_out=1 (bottom). The results for the uncalibrated measurement mic_raw are the same and not shown.
Left: calibrated motor current (current_mot) under an impulse on the input mot_max , when the motor is enabled (mot_enabled=1, blue) and when it is disabled (mot_enabled=0, yellow). Right: measurements of the calibrated motor current (current_mot) for different values of mot_max, when the motor is enabled (mot_enabled=1, blue) and when it is disabled (mot_enabled=0, yellow). The behaviour of the uncalibrated measurement current_mot_raw is the same and not shown.
Left: measurements from the tunnel barometers over the span of 3 hours, showing the effect of variations in the local atmospheric pressure at our facility in Zurich. The fans are powered off, and all chamber inputs and parameters are kept constant. Right: drift in the barometer sensors, visible when controlling for the effect of ambient atmospheric pressure, i.e., by subtracting the pressure_ambient measurement, which is unaffected by the other chamber variables (see also Figure 13).
| Variable | Description |
|---|---|
hatch | The set position of the hatch, in degrees. The hatch is closed at 0º and open at ± 45º. |
hatch_angle | The position of the hatch, in degrees, as measured by the encoder of the motor. |
mot_steps | The steps-per-revolution of the stepper motor controlling the hatch. Higher values mean a higher motor resolution, i.e., more precise positioning (Figure 6). |
mot_enabled | Enables (1) or disables (0) the motor controlling the hatch. If the motor is disabled (0), setting hatch will have no effect on the actual position of the hatch (Figure 6). |
mot_max | Regulates the maximum current drawn by the motor controlling the hatch. At low current levels the motor may lose torque and start missing steps, resulting in a mismatch between the set position hatch and the actual hatch angle (Figure 6). |
current_mot | The measurement (in Amperes) of the electric current drawn by the motor controlling the hatch (Figure 12). |
current_mot_raw | The uncalibrated measurement, i.e., the raw ADC output, corresponding to the measurement current_mot. |
offset_current_mot | The reference voltage (offset) of the ADC producing the current_mot and current_mot_raw measurements. The actual reference voltage (in Volts) is given by 5 \times \frac{\text{offset\_current\_mot}}{4095}. Because the signal from the current sensor is passed through an inverting amplifier, higher values of offset_current_mot result in higher values of current_mot_raw (Figure 9). |
sps_current_mot | The data rate of the ADC producing the current_mot and current_mot_raw measurements. Lower values mean the ADC accumulates more readings to produce a single measurement, reducing noise but also lowering the measurement speed (Figure 9). |
res_current_mot | The resolution of the ADC producing the current_mot and current_mot_raw measurements. Higher values mean a higher resolution, where a smaller voltage range is mapped to the ADC output range \{-32768, \ldots, 32767\}. The reading will saturate, i.e., clamp at -32768 or 32767, if the input voltage exceeds the set range (Figure 9). |
load_in | The load of the intake fan, corresponding to the duty cycle of the pulse-width-modulation (PWM) signal that controls its speed. At higher values, the fan consumes more power and turns faster. At 0, the complete fan is powered off, including the tachometer; the measurement of fan speed (rpm_in) remains constant at the last measured value. |
rpm_in | The speed of the intake fan in revolutions per minute. |
res_rpm_in | The resolution of the tachometer that measures the speed of the intake fan (Figure 4), where 1 corresponds to microseconds (higher resolution) and 0 to milliseconds (lower resolution). |
load_out | The load of the exhaust fan, corresponding to the duty cycle of the pulse-width-modulation (PWM) signal that controls its speed. At higher values, the fan consumes more power and turns faster. At 0, the complete fan is powered off, including the tachometer; the measurement of fan speed (rpm_out) remains constant at the last measured value. |
rpm_out | The speed of the exhaust fan in revolutions per minute. |
res_rpm_out | The resolution of the tachometer that measures the speed of the exhaust fan (Figure 4), where 1 corresponds to microseconds (higher resolution) and 0 to milliseconds (lower resolution). |
pressure_intake | The air pressure, in pascals, measured by the barometer placed at the tunnel intake. |
osr_pressure_intake | The oversampling rate of the intake barometer, which determines how many consecutive readings are averaged to produce a single measurement (Figure 8). |
pressure_ambient | The air pressure, in pascals, measured by the outer barometer. This is the ambient pressure outside the chamber. |
osr_pressure_ambient | The oversampling rate of the ambient barometer, which determines how many consecutive readings are averaged to produce a single measurement (Figure 8). |
pressure_downwind | The air pressure, in pascals, measured by the barometer inside the tunnel placed facing away from the airflow. |
osr_pressure_downwind | The oversampling rate of the downwind barometer, which determines how many consecutive readings are averaged to produce a single measurement (Figure 8). |
pressure_upwind | The air pressure, in pascals, measured by the barometer inside the tunnel placed facing into the airflow. |
osr_pressure_upwind | The oversampling rate of the upwind barometer, which determines how many consecutive readings are averaged to produce a single measurement (Figure 8). |
current_in | The measurement of electric current drawn by the intake fan, in Amperes. |
current_in_raw | The uncalibrated measurement, i.e., the raw ADC output, corresponding to the measurement current_in. |
offset_current_in | The reference voltage (offset) of the ADC producing the current_in and current_in_raw measurements. The actual reference voltage (in Volts) is given by 5 \times \frac{\text{offset\_current\_in}}{4095}. Because the signal from the current sensor is passed through an inverting amplifier, higher values of offset_current_in result in higher values of current_in_raw (Figure 9). |
sps_current_in | The data rate of the ADC producing the current_in and current_in_raw measurements. Lower values mean the ADC accumulates more readings to produce a single measurement, reducing noise but also lowering the measurement speed (Figure 9). |
res_current_in | The resolution of the ADC producing the current_in and current_in_raw measurements. Higher values mean a higher resolution, where a smaller voltage range is mapped to the ADC output range [-32768, 32767]. The reading will saturate, i.e., clamp at -32768 or 32767, if the input voltage exceeds the set range (Figure 9). |
current_out | The measurement of electric current drawn by the exhaust fan, in Amperes. |
current_out_raw | The uncalibrated measurement, i.e., the raw ADC output, corresponding to the measurement current_out. |
offset_current_out | The reference voltage (offset) of the ADC producing the current_out and current_out_raw measurements. The actual reference voltage (in Volts) is given by 5 \times \frac{\text{offset\_current\_out}}{4095}. Because the signal from the current sensor is passed through an inverting amplifier, higher values of offset_current_out result in higher values of current_out_raw (Figure 9). |
sps_current_out | The data rate of the ADC producing the current_out and current_out_raw measurements. Lower values mean the ADC accumulates more readings to produce a single measurement, reducing noise but also lowering the measurement speed (Figure 9). |
res_current_out | The resolution of the ADC producing the current_out and current_out_raw measurements. Higher values mean a higher resolution, where a smaller voltage range is mapped to the ADC output range [-32768, 32767]. The reading will saturate, i.e., clamp at -32768 or 32767, if the input voltage exceeds the set range (Figure 9). |
mic | The measurement of the sound level captured by the microphone, in Volts. |
mic_raw | The uncalibrated measurement, i.e., the raw ADC output, corresponding to the measurement mic. |
offset_mic | The reference voltage (offset) of the ADC producing the mic and mic_raw measurements. The actual reference voltage (in Volts) is given by 5 \times \frac{\text{offset\_mic}}{4095}. Higher values of offset_mic result in lower values of mic_raw (Figure 10). |
sps_mic | The data rate of the ADC producing the mic and mic_raw measurements. Lower values mean the ADC accumulates more readings to produce a single measurement, reducing noise but also lowering the measurement speed (Figure 10). |
res_mic | The resolution of the ADC producing the mic and mic_raw measurements. Higher values mean a higher resolution, where a smaller voltage range is mapped to the ADC output range [-32768, 32767]. The reading will saturate, i.e., clamp at -32768 or 32767, if the input voltage exceeds the set range (Figure 10). |