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title	[Sensor] I am curious about 3 axis acceleration sensor.
name	admin 11-08-29 21:44
Hello, customer? Thank you for using our NEWTC product. Detailed information is available at product manual. For more information, please see datasheet of chip. - Below - http://www.newtc.co.kr/board/data/pds/AM_3AXIS_3축센서테스트보드_Ver_2.pdf. To explain briefly, in case of 1.5g by standard of 1.65V, value of voltage will change to 800mV/g. In case of 1g, g is an abbreviation of gravity and means acceleration of gravity. Attached picture is extracted from MMA7260Q datasheet which is the core IC of a module. If you look at the picture carefully, you can understand what it is. First, you have to learn that acceleration = Static acceleration + Dynamic acceleration. You have to assume that Dynamic acceleration does not generate severely if you intend to measure only angle. That is because it is difficult to pick out static acceleration separately in this module. In other words, if sensor moves very slowly, very small Dynamic acceleration only generates and thus total value reaches approximating value to static acceleration and so you can use it for measuring the angle as you desire. You might as well as shown in the figure if you correspond -90 degree ~ +90 degree to -1g ~ +1g. Please see the below for conversion to gradient. - Below - http://www.newtc.co.kr/board/view.phpid=pds&page=1&sn1=&divpage=1&sn=off&ss=on&sc=off&keyword=formula&select_arrange=headnum&desc=asc&no=121 That is to say, you can gain the value of voltage from the axis of X, Y and Z respectively. In case of 0g, you can get 1.65V. In the mode of 1.5g, output voltage per g changes by roughly 800mV. The module is manufactured so that it is basically set to the mode of 1.5g even if nothing is connected to gSelect. Of course, if you change the mode, the module will operate by the altered mode. And Z axis will be 1g in case of parallel placement. Therefore, we can gain 1.65V + 800mV = 2.45V. Even if we set to 0g, as a matter of fact, it is difficult to set an exact parallel. In this case, offset error can occur. The chip was very accurate at that time when it was manufactured because the chip is cut by laser in producing but, slightly an error can occur resulting from transportation, mechanic stress and temperature. If you read the manual linked below, you can see the same information. - Below - http://www.freescale.com/files/sensors/doc/app_note/AN3447.pdfWT_TYPE=Application%20Notes&WT_VENDOR=FREESCALE&WT_FILE_FORMAT=pdf&WT_ASSET=Documentation However, algorithm to compensate this error is needed for this situation. First, you need to set 0g. Every chip can have different condition and the condition of the chip can be changed if it is given much stress after it was produced. For this reason, it is recommended that you prepare for function for the purpose of offset error correction to control 0g provided that 0g is an important issue. However exactly the chip may be placed on the flat ground, actually the chip can be inclined slightly and so you can take 0g which is an intermediate point of them getting the least value and the highest value if you turn slowly on each axis to the direction by one cycle. There are other ideas and please read the manual for them. In addition, it is recommended that you try to read the datasheet of MMA7260Q for exact utilization. If you search mma7260q datasheet in search engine, you can easily find it. Below is the answer related with measurement of distance using acceleration sensor. Please refer to it. - Measuring the distance using acceleration sensor - http://www.newtc.co.kr/board/view.phpid=qna&page=1&sn1=on&divpage=2&sn=on&ss=off&sc=off&keyword=조승근&select_arrange=headnum&desc=asc&no=9557 Thank you.