Some Results of Experimental Studies of Airflow Velocity Sensors with a Sensitive Element in the Form of a Deflecting Flap and Transformer-Based Angle Conversion
Abstract Generated abstract
This paper reports laboratory and production tests of a prototype airflow velocity sensor intended for mine ventilation monitoring, using a deflecting flap as the sensitive element and a transformer-based angle converter. The authors describe the prototype design, its electrical parameters, and an approximate static characteristic relating output voltage to airflow velocity while accounting for flap deflection effects. Experimental results show the sensor output dependence on velocity and indicate that its transient behavior is oscillatory, with insufficient damping of the moving system under the tested conditions. Production trials in a main fan channel demonstrated remote recording of airflow velocity and recalculated flow rate using an indicating and regulating instrument.
Full Text
Some Results of Experimental Studies of Airflow Velocity Sensors with a Sensitive Element—a Deflecting Flap—and a Transformer-Based Angle Converter
A. E. Simakov, B. M. Titov, M. A. Tyryshkin
(Presented by the scientific seminar of the Department of Automation and Telemechanics)
For the automation of ventilation in the underground workings of a mining enterprise (or simply for operational monitoring), a system for automatic monitoring of the state of the mine atmosphere is necessary.
One of the parameters characterizing ventilation is the velocity of the airflow.
Works [1, 2] have shown the possibility of using, for measuring flow velocity, sensors with a sensitive element—a deflecting flap—and a transformer-based angle converter. Such sensors are structurally simple and make it possible to measure flow velocities of the most varied ranges (for example, 0–1; 0–5; 0–10; etc. m/sec), i.e., they cover the regions of all possible flow velocities in mine workings.
The placement of the armature below the excitation pole and its vibrational operating mode make it possible to substantially reduce the influence of bearing resistance on the sensor characteristics.
The theoretical foundations for constructing such sensors are given in works [1, 2, 3].
In the present work, some results are presented from tests of a prototype sensor under laboratory and production conditions.
The prototype was manufactured in the workshops of the Vakhrushev mine of the “Kuzbassugol” combine.
The counteracting moment is produced by shifting the center of gravity below the axis of rotation. The sensitive element—the flap—deflected in a guide channel of constant cross section. The velocity vector did not remain normal to the plane of the flap during its deflection.
The electrical parameters of the sensor were: \(U_{\text{in}} = 36\) volts; \(U_{\text{out max}} = 8\) volts; number of turns of the excitation winding—2000, of the signal windings—600.
The laboratory tests were carried out on a fan installation [4], consisting of an axial fan with blades adjustable in pitch while running, a control panel, and a metal pipeline.
For an unbalanced moving system, when the counteracting moment is produced by shifting the center of gravity below the axis of rotation and when the magnetic fluxes of bulging and leakage
are not taken into account, the static characteristic of the sensor is approximately determined by the following relation:
\[ U_{\text{out}} \simeq \kappa_1 \kappa_2(\alpha)\,\arc\sin \frac{v^2}{v_{\max}^2 \sin \alpha_{\max}}, \tag{1} \]
\[ \kappa_1=\frac{\omega \Phi_0 w_c}{\sqrt{2}}, \]
where \(\omega\) is the angular frequency of the power supply;
\(\Phi_0\) is the amplitude of the flux in the pole gap of the excitation winding;
\(w_c\) is the number of turns of the signal winding;
\(v\) is the measured flow velocity;
\(v_{\max}\) is the upper measurement limit of the given sensor;
\(\alpha\) is the deflection angle of the moving system;
\(\alpha_{\max}\) is the maximum deflection angle of the sensor armature (corresponding to \(v_{\max}\));
\(\kappa_2(\alpha)\) is a coefficient accounting for the deviation of the vector of the measured velocity from the normal to the plane of the flap when it is deflected.
The static characteristic of the experimental specimen is shown in Fig. 1. From the characteristic it is seen that \(\kappa_2(\alpha)<1\).
In the graph: vertical axis—“Voltage at output, V”; horizontal axis—“Air velocity, m/s.”
Fig. 1. Dependence of the sensor output voltage on the flow velocity
The transient functions of the sensor are shown in Fig. 2. Transient function 2 was oscillographically recorded when the sensing element was released (the moving system had previously been braked). The flow velocity in the channel was steady (\(\sim 3\ \text{m/s}\)).
Transient function 1 was oscillographically recorded from the moment the slide valve of the channel was closed upstream of the sensor installation point. From the oscillograms it is seen that the sensor is an oscillatory element.
In accordance with the differential equation of the sensor [3]:
\[ T_2^2 \frac{d^2 \Delta U_{\text{out}}}{dt^2} + T_1 \frac{d \Delta U_{\text{out}}}{dt} + \Delta U_{\text{out}} = \kappa_y \Delta v. \tag{2} \]
We therefore have
\[ T_1 < 2T_2. \tag{3} \]
This condition was satisfied, since the oscillations of the moving system were not damped.
In (2) \(K_3\) is the sensor transfer coefficient with respect to velocity (V·s/m); \(T_1\) and \(T_2\) are time constants (s).
Production tests of the sensor were carried out in the channel of the main fan of one of the mines of the Kiselevskugol Trust.
Remote monitoring of the flow velocity and flow rate was performed using the indicating and regulating instrument N-340. A recording on the chart tape of the flow velocity and the recalculated air flow rate is shown in Fig. 3.
Fig. 2. Transient characteristics of the sensor:
a — velocity step and the transient characteristic 1 corresponding to this step;
b — transient characteristics.
Labels in the figure:
a) “air velocity, m/s”; \(t\), s.
b) “sensor output voltage, V”; \(t\), s.
Fig. 3. Recording on chart tape of the velocity (flow rate) of air in the channel of the main fan installation.
Labels in the figure:
\(Q\), m\(^3\)/s; \(v\), m/s; “fan start”; “normal operation”; “chart tape travel speed 3.3 mm/s”; “velocity and flow-rate scale”: \(m_v = 0.4\ \frac{\mathrm{m/s}}{\mathrm{mm}}\), \(m_Q = 2.06\ \frac{\mathrm{m^3/s}}{\mathrm{mm}}\).
References
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M. A. Tyryshkin. On the measurement of the velocity of airflows in mine workings by a transformer-based sensor of the deflection angle. Izv. vuzov, Mining Journal, No. 4, 1962.
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M. A. Tyryshkin. Velocity sensors for ventilation flows with a sensitive element—a deflecting flap—and a transformer-based angle converter. Izv. vuzov, Mining Journal, No. 12, 1963.
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M. A. Tyryshkin. Velocity sensors for mine ventilation flows. Candidate dissertation, Sverdlovsk, 1964.
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B. M. Titov, N. I. Petrov. A device for automatic regulation and remote reversal of axial fans by turning the impeller blades while running. Izv. vuzov, Mining Journal, No. 10, 1964.