Motion control and industrial automation systems have brought many challenges to design engineers. For example, they must resolve excessive dirt and dust found in factory settings. In addition, conveyor belts and pick-and-place systems may experience high vibration or shock peaks, which threatens the stability of the circuit sensor. The selected magnetic sensing system must have excellent durability to ensure long-term accuracy and reliability within the application range.

During project planning, design engineers should conduct a thorough review of the environmental, mechanical, electrical and magnetic parameters of industrial applications. Engineers should analyze the full magnetic circuit for industrial applications-including sensors and magnetic actuators. Taking all the key factors into consideration, engineers may recommend powerful custom sensors to meet the unique requirements of industrial automation systems.

This episode will discuss how to select highly accurate and reliable sensors for industrial automation applications. After defining and describing the advantages of several analog and digital sensors, it will provide examples of industrial applications that utilize these devices.

Analog Rotary and Linear Hall Effect Sensors provide stability and accuracy

The analog sensor allows the end user to get instant feedback about the position of the magnet in the industrial automation system. In the past, analog Hall Effect sensors measured the magnetic flux density of magnets and were greatly affected by the temperature value of the application. The latest developments in analog Hall Effect technology enable the hall effect chip to measure the angle of the flux field instead of the traditional amplitude, thereby greatly reducing its sensitivity to temperature changes. Now, Hall Effect sensors can provide a very stable analog output over a wide temperature range.

The following Hall Effect sensors are well suited for custom analog sensing applications:

Rotary Hall Effect Sensor

The Rotary Hall Effect sensor does not use any moving parts. This semiconductor-based sensor combines a Hall Effect sensing element with a circuit to provide an analog output signal corresponding to the change in the rotating magnetic field. Rotary Hall Effect sensors provide two output options: analog or pulse width modulation (PWM). The device is programmable, so engineers can associate a specific output voltage or PWM with a precise degree of rotation.

Multiple programming points can be rotated up to 360 degrees. Each programming point represents the voltage or PWM output value corresponding to a given magnetic field angle. This produces a high-precision, high-resolution ratio measurement output signal relative to the degree of rotation.

Advantages:

Not subject to resistance value changes or mechanical wear like mechanical rotation or resistance film rotation devices;

Provides excellent stability under normal working temperature up to +105°C;

Provides 0.5-4.5 VDC output or 0-360 degree rotation accuracy with PWM duty cycle 10-90%.

Application:

Replacing the resistance film and potentiometer mechanical device;

Motion control applications include measuring the angle of the flapper valve in the fluid and accurately controlling the flow rate;

Checking the position of the dial in the control circuit.

Linear Hall Effect Sensor

Linear Hall Effect sensors measure the linear movement of the magnetic field, not the rotation. The sensor can be programmed for a set output voltage, which is proportional to a given distance traveled. (The output options are the same as the rotary Hall Effect sensor.) The sensor uses a single Hall Effect chip to measure the linear motion and relative magnetic flux angle of the magnetic actuator, with a maximum stroke of 30 mm. This results in a proportional output signal relative to the precise movement of the sensor.

Advantages:

Sensors and actuators can be placed in the final installation area of the application (including all magnetic effects of the surrounding environment);

This mounting position allows engineers to optimize the output signal of the application to correspond to the direction of the magnetic flux as the magnet rotates.

Application:

Can be used as a liquid level sensor to monitor the liquid level;

The sensor detects the position of the moving float, which is equipped with a magnet;

Provide very precise position tolerances for automatic pick-and-place systems;

The reed and Hall Effect provide highly reliable digital sensing.

Industrial automation users prefer digital output if they want to verify that an object (such as an elevator door) is in the correct position. The following digital sensors provide excellent reliability in custom magnetic induction applications:

Reed Switch

The contacts of the reed switch are sealed in a glass tube with precious metal contact materials. The electrical switch does not require any power source to operate.

Advantages:

Unaffected by humidity and other environmental hazards, it can achieve reliable operation of millions of cycles

Application:

Logic level electrical load controlled by microprocessor;

Digital opening/closing applications, such as door closing or position detection systems in the industrial/motion control market.

Digital Hall Effect Sensor

These sensors combine Hall Effect sensing elements with circuits to provide digital on/off output signals corresponding to changes in the magnetic field without using any moving parts. The active circuit of the Hall-effect device always draws a small amount of current.

Advantages:

Provide high reliability;

Programmable to activate under a given magnetic field tolerance to meet precise sensing requirements.

Application:

Limited to industrial and motion control applications with low DC voltage and current values;

Widely used in high-speed sensing applications, such as speed sensing on conveyors.

Conclusion 

There are a lot of environmental hazards in industrial automation and motion control environments. Designing a magnetic circuit that integrates a powerful magnetic sensor is the key to providing accurate and reliable industrial automation solutions. For some industrial applications, a customized magnetic sensor may be required to achieve long-term reliability. Reed switches and Hall Effect sensors are ideal for digital applications that require special reliability, such as elevator door closing detection systems. Rotary and linear hall effect sensors enhance the stability and accuracy of custom analog applications such as fluid flow and automatic pick-and-place systems.