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With an inclinometer you can measure angles and slopes between a surface and the horizon. Such devices are useful tools for every handyman or renovator. We examined one of the cheapest digital inclinometers you can buy. |
Introduction to this digital inclinometer
Of course you can also use an app!
The Google Play Store and the Apple App Store are full of apps by which you can turn your smartphone into an inclinometer. But if you don't want to use your hundreds of euros costing smartphone in the dusty and electronics hazardous environment of a home improvement or a workplace, you can also buy a separate inclinometer. Thanks to the Chinese electronics manufacturers, these devices are for sale for less than ten euros nowadays.
Nameless, but well cared for
Most articles we open with the paragraph 'Introduction to device yyy from brand xxx'. This is not possible here, because this digital inclinometer is offered unbranded and doesn't even have a type number on it. The only indication on the device is 'DIGITAL INCLINOMETER'. Moreover, the price varies: you will find dozens of stores on the Internet with prices between € 6,44 and € 39,95. All this does not seem promising, but when you unpack the cardboard box you will notice that this device looks very well cared for. It comes in a sturdy semi-transparent plastic box with, surprisingly enough, a small screwdriver. This appears to be necessary to open the battery compartment in which you need to mount two 1.5 V type AAA cells. The included manual is bilingual Chinese/English and looks neat.
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| The device is delivered in a sturdy plastic box. (© 2019 Jos Verstraten) |
With its dimensions of 55 mm x 55 mm x 25 mm and its weight of 92 g, the device fits easily in your hand. The case is made of aluminium and the front and back are screwed on with four small screws. Two small but very strong neodymium magnets are placed in the bottom of the case, so that you can click the device on, for example, an iron bar while aligning this bar.
At the bottom there are three small push buttons. However, you need to apply a lot of force to these buttons to activate them.
With the left one you turn the device on or off. By the way, the device switches off automatically after five minutes of inactivity. A short press on the middle button freezes the readout, so you can read the device quietly. If you press this button for a longer time, the device switches from measuring in angular degrees to measuring in percent. An angle of 45° is taken as the 100% reference. In this way you can also measure slopes. Use the right button to switch on the REL function. The instantaneous readout is then stored as a zero reference in the device and all measurements are referred to this zero. If you press this button for a longer time, the backlight of the display turns on, so that you can read the device even in the dark.
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| The inclinometer is housed in an easy-to-handle case. (© 2019 Jos Verstraten) |
Rotate 180 degrees and it also works
It should be noted that you can rotate the unit by 180°. The display also rotates 180°, so that you can read the inclinometer without difficulty.
The specifications
According to the (unknown) manufacturer, this digital inclinometer has the following specifications:
- Measuring range: 4 x 90°
- Resolution: ±0.05°
- Accuracy: ±0.2°
- Repeatability: ±0.1°
- Modes: absolute and relative
- Units: angular degrees and percentages
- Power supply: 2 x 1.5 V type AAA battery
- Operating temperature: 0 °C ~ +40 °C
The electronics in the device
There is a small PCB in the device, see the picture below, with surprisingly few components. On the side that rests against the front you can see the three switches K1, K2 and K3 etched on the PCB. Above them are the contacts that press against the conductive rubber strip of the display. On the other side of the PCB, the microprocessor is covered with black protection paste.
The most important part can be seen above on the right, a MXA2500E 'low noise and low cost dual axis MEMS accelerometer' from MEMSIC. This is the part that measures the angle at which you hold the inclinometer.
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| The two sides of the PCB. (© 2019 Jos Verstraten) |
The accelerometer used in this inclinometer measures the angle at which the sensor stands in relation to the horizon by applying an electro-thermal principle. This principle is explained by the schematic cross-section through the sensor below. To make it not too difficult, we will discuss the operation of a one-dimensional accelerometer. The sensor consists of a completely airtight sealed very small space, a so-called 'cavity', in which a gas is enclosed. In the middle of the cavity there is a very small heating element. To the left and right of this element, at exactly the same distance, there are two extremely small and very sensitive temperature sensors.
When the sensor is completely horizontal, a static state will occur in the gas, with the heated molecules forming an even layer at the top of the cavity. The two sensors measure identical temperatures and generate identical voltages.
However, if the sensor tilts to the bottom right, gravity will cause the hot and therefore lighter molecules to accumulate in the top left corner of the cavity. The two sensors measure different temperatures and from the different sensor voltages the electronics can derive the angle at which the sensor is tilted.
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| The basic operation of a thermal accelerometer. (© MEMSIC) |
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| Using two perpendicular axes increases accuracy. (© MEMSIC) |
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| The internal block diagram of the MXA2500E. (© MEMSIC) |
Testing the digital inclinometer
How to test such a device?
To test a device, you need another device that is at least ten times more accurate. In this case we don't have one. Fortunately, geometry offers an elegant solution. We used a CAD program to draw an accurate star with 36 points. A circle is, by definition, divided into 360°. So the points of the star are 10° apart. With a poster-print program we have printed this star on twelve sheets of A4 and carefully glued them together. Afterwards, a perpendicular line was drawn on a flat wall using a plumb bob and and the poster was accurately glued to the wall with its own perpendicular line exactly on the perpendicular line on the wall. In this way it was possible to accurately measure angles of 10°, 20° and so on up to 90°. Place a straight long metal ruler exactly on two opposite points of the star and place the inclinometer on the ruler. The device should now measure the drawn angle.
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| The measurement method we applied. (© 2019 Jos Verstraten) |
In the table below we have summarized the results of measuring nine angles. As this table shows, the maximum error measured is 1%. The specified accuracy of ±0.2° is achieved with almost all measurements.
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| The results of the test of this inclinometer. (© 2019 Jos Verstraten) |
Our opinion about this digital inclinometer
We are very satisfied with the appearance, construction and accuracy of this digital inclinometer. For anyone who regularly needs to measure angles in a building or mechanical construction, such a handy device is an extra. Just one advice: in view of the large price differences, it is very wise to first extensively googling to the supplier with the lowest price before ordering!
Digital Inclinometer
