Resolution and Accuracy of Tilt Sensors

Accuracy and resolution of tilt sensors

Resolution refers to the sensor in the measurement range can detect and resolve the smallest change in the measured value. The accuracy refers to the error between the angle measured by the sensor and the real angle.

The relationship between precision and resolution with examples 

Take the familiar vernier calipers. We often say that the accuracy of the vernier caliper is 0.1mm, in fact, this statement is not correct, it should be said that the resolution of the vernier caliper is 0.1mm. That is, when the change in length is 0.1mm, Can our eyes see it, tell it apart. The accuracy of the vernier caliper, because the accuracy represents the difference between the measured value and the true value, the accuracy is related to many factors. For example, temperature causes thermal expansion and contraction, when we see a change of 0.1mm, the real may be 0.09mm, such as the caliper bending, or the caliper engraving line is not particularly uniform, will lead to poor accuracy, but the resolution is still 0.1mm. To improve the accuracy of the measurement, we must first improve the resolution of the measurement, if the resolution can not be distinguished, then the accuracy from where to start. Resolution is the limit of accuracy, improve the resolution at the same time to eliminate the impact of other factors on the accuracy, in order to effectively improve the final accuracy.

The angle sensor based on acceleration principle is illustrated in detail. It is the measurement of gravitational acceleration on the sensitive axis of the acceleration sensor into angle data, that is, the angle value and the acceleration value into a sine relationship.

The resolution of tilt sensors are also often referred to as sensitivity. It is mainly caused by the noise of the sensor. The noise equivalent angular change is called the angular resolution. Because the size of the noise is related to the frequency response, the higher the frequency response, the greater the noise. The resolution of the sensor can be improved effectively by taking effective measures to suppress the noise. After the resolution is improved, there is a chance to compensate for the adverse impact of other factors on the accuracy.

Other factors affecting the accuracy of tilt sensors

Of course, there are many factors that affect the accuracy of tilt sensors, in addition to the most important resolution, but also include:

Zero bias–depending on the characteristics of the core sensitive device itself, it means that the sensor in the absence of angle input (such as absolute horizontal plane), the sensor measurement output is not zero, the actual output angle value is zero bias.

Nonlinearity— can be corrected later, depending on the number of correction points. The more correction points, the better the nonlinearity.

Horizontal axis error— refers to the error caused by coupling to the output signal of the sensor when the sensor applies a certain acceleration perpendicular to its sensitive axis or tilts at a certain angle.

Input shaft non-alignment – refers to the installation deviation of the sensor in the actual installation process, which actually includes the input shaft non-alignment and vertical shaft non-alignment errors.

Sum up

We use specific tilt sensors products to look at the relationship between resolution and accuracy, for example, our ER-TS-12200-Modbus, from the main parameters can be seen, its resolution is 0.0005°, that is, within the measurement range of ±30° can detect and distinguish the smallest change value measured is 0.0005°, the resolution is quite high. The comprehensive accuracy within the full temperature of -40~85° can reach 0.001°, because its resolution has been improved a lot, so its accuracy is naturally improved. 

In the following figure, the main parameters of ER-TS-3160VO Low cost Voltage Type Single Axis Tilt Sensor, in different measurement ranges, its resolution is not the same, at ±10° its resolution can reach 0.001°, the accuracy is 0.01°. By comparing the parameters of these two products, we can see a relationship between resolution and accuracy. The resolution is low, the accuracy is relatively low, if the resolution is improved, the accuracy will be improved accordingly.

How do MEMS Tilt Sensors Work?

 MEMS tilt sensors, as the name suggests, are tilt sensors manufactured by MEMS (microelectromechanical system) technology, which has the obvious advantage of very accurate measurement.

Here we explain the principle of MEMS tilt sensor through an example.

In simple terms, the MEMS tilt sensor is a non-contact measurement of the inclination of the target object through the Earth's gravity. In essence, the tilt sensor measures acceleration, especially gravitational acceleration, so it has an integrated accelerometer chip. The acceleration sensor chip consists of a MEMS sensing component and a peripheral signal processing circuit. The MEMS sensing components are shown as follows:

The blue part of the MEMS sensing component is mobile, while the red part is fixed. When accelerating or decelerating, the blue part will move left or right, and the capacitance between the blue and red parts will change accordingly. Acceleration can be determined by measuring the capacitors C1 and C2. As shown in the picture below:

That is, the acceleration or deceleration that occurs when the object is tilted causes the movable part of the MEMS sensing component to move to one side, as shown below:

It can be seen from this principle that the MEMS sensing component is very sensitive to vibration during the measurement process, and the vibration of the measured object will affect the measurement result. So filters must be added to eliminate interference beyond a certain frequency. Some MEMS tilt sensor manufacturers will also be equipped with filters according to user needs. There are two types of filters: Butterworth filters and Critically damped filters. Batvots is more suitable for measuring non-moving, high vibration objects, such as large drilling platforms; Critical damping filters are more suitable for measuring moving objects, such as engineering vehicles, agricultural vehicles, etc. The vast majority of tilt sensors on the market today are equipped with Butterwart filters only, or no filters at all.

Ericco’s ER-TS-3160VO built-in (MEMS) solid pendulum measures the change of static gravity field, which is converted into the change of inclination, and the change is output through the voltage (0~10V, 0~5V optional).

If you want to learn more about MEMS tilt sensors or buy

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