BAROMETER/ALTIMETER ML36S USER’S GUIDE CENTRE FOR MICROCOMPUTER APPLICATIONS
http://www.cma-science.nl
Short description The Barometer/Altimeter ML36s measures atmospheric pressure in the range of 300 hPa to 1,100 hPa and calculates the respective altitude in meters assuming that the average pressure exerted at sea level by the atmosphere is 1013.25 hPa (1 atmosphere). The sensing element of the sensor is mounted inside the sensor housing. The sensor’s electronics has an automatic internal temperature compensation to minimize the effect of ambient temperature changes on the data. The pressure sensor is fairly durable but it is designed only for use with non‐
corrosive, non‐ionic working gasses such as air, dry gases and the like. Do not get it wet. The Barometer/Altimeter is an I2C digital sensor, which gives calibrated values of the measured quantity. This sensor can only be connected to special interfaces that support I2C digital sensors like the CMA MoLab interface. The sensor cable needed to connect the sensor to an interface is not supplied with the sensor (sensor cables are supplied with interfaces). Sensor specifications The Barometer/Altimeter ML36s is a digital sensor that converts the measured barometric pressure value to a digital value via 19‐bit analog‐to‐digital conversion. The resolution of the sensor is ± 0.01 hPa. The maximal sampling frequency of the sensor is 10 Hz (samples per second). The altitude is calculated based on the following formula: Altitude = 44,300*(1‐(p/p0)^(1/5.255)) Where p is the measured barometric pressure, and p0 is the sea level standard
atmospheric pressure, which is 1,013.25 hPa. Practical information  Allow the outside air to easily flow onto the sensor element.  If you use the sensor in a closed and purely ventilated room, the sensor can give incorrect measurements.  The maximum pressure that this sensor can tolerate is 1,100 hPa.  Do not use the sensor in a hot air flow.  Do not allow water or any liquids come into the sensor. 2 | ML36s Barometer/Altimeter User’s Guide Collecting data This Barometer/Altimeter works only with specific interfaces. The sensor will be automatically detected when connected to such an interface. For detailed information about measurements with sensors consult the User Manuals of the interface and the Coach 6 software. Calibration The Barometer is supplied with a factory calibration in hPa. The Altimeter is calibrated in meters, which values are calculated based on conversion of the measured pressure assuming 1 atmosphere (1013.25 hPa) of pressure at sea level. In that way the sensor gives relative rather than absolute values of altitude. If the altitude of your measurement location is known, values can by adjusted by using the Set to value option in the Coach 6 program. Note: The value for Barometric pressure reported by airports and weather stations is usually given for the pressure at sea level i.e. pressure after it has been adjusted to its equivalent at sea level. The value obtained by this sensor will be the pressure at its current location. Suggested experiments The Barometer/Altimeter can be used in various experiments such as:  Measurements of the air pressure over a longer period of time (weather studies).  Measurements of the pressure in liquids by connecting the sensor to a tube, which is submerged in a solution.  Measurements of pressure differences between different floors of buildings.  Altitude investigations. Figure 1. Explore the pressure inside an empty, sealed, plastic bottle, before and after squeezing the bottle. ML36s Barometer/Altimeter User’s Guide | 3 Technical Specifications Sensor kind Digital on‐sensor digital conversion (19‐bits resolution, communication via I2C) Measuring range Barometric pressure: 300 hPa .. 1100 hPa Calculated range Altitude: ‐ 1000 .. 9000 m Resolution ± 0.01 hPa ± 0.25 m Uncertainty (accuracy) Typical ±1.0 hPa at 0 to 65℃, Max. ± 3.0 hPa Reading time Typical 100 ms Maximal sampling rate 10 Hz Dimensions Sensor housing: 37 x 18 x 16 mm Connection 5‐pins mini jack plug Warranty: The Barometer/Altimeter ML36s is warranted to be free from defects in materials and workmanship for a period of 12 months from the date of purchase provided that it has been used under normal laboratory conditions. This warranty does not apply if the sensor has been damaged by accident or misuse. Note: This product is to be used for educational purposes only. It is not appropriate for industrial, medical, research, or commercial applications. Rev. 17/11/2011
4 | ML36s Barometer/Altimeter User’s Guide