MPXM2102AS datasheet(449/670 Pages) MOTOROLA

449 / 670 page

AN1516

3–303

Motorola Sensor Device Data

www.motorola.com/semiconductors

Open Pipe Before

Calibration

Control Module

Pressure

Sensor

Air

Liquid Level

in the Pipe

Electrical

Pump

AC Line

Reference

Level

Figure 3. Liquid Level Monitoring

LEVEL SENSING THEORY

If a pipe is placed vertically, with one end dipped into a liquid

and the other end opened, the level in the pipe will be exactly

the same as the level in the tank. However, if the upper end of

the pipe is closed off and some air volume is trapped, the

pressure in the pipe will vary proportionally with the liquid level

change in the tank.

For example, if we assume that the liquid is water and that

the water level rises in the tank by 10 mm, then the pressure

in the pipe will increase by that same value (10 mm of water).

A gauge pressure sensor has one side connected to the

pipe (pressure side) and the other side open to ambient (in this

case, atmospheric) pressure. The pressure difference which

corresponds to the change in the tank level is measured by the

pressure sensor.

PRESSURE SENSOR CHOICE

In this example, a level sensing of 10 mm of water is desired.

The equivalent pressure in kilo pascals is 0.09806 kPa. In this

case, Motorola’s temperature compensated 0 – 10 kPa,

MPXM2010GS is an excellent choice. The sensor output, with

a pressure of 0.09806 kPa applied, will result in 2.0 mV/kPa

x 0.09806 = 0.196 mV.

The sensing system is designed with an amplifier gain of

about 1000. Thus, the conditioned signal voltage given by the

module is 1000 x 0.196 mV = 0.196 V with 10 mm – H2O

pressure.

Table 1. Liquid Level Sensors

METHOD

SENSOR

ADVANTAGE

DISADVANTAGES

Liquid weight

Magnetoresitive

Low power, no active electronic

Low resolution, range limited

Magnetoresitive

Very high resolution

Complex electronic

Ultrasonic

Easy to install

Need high power, low accuracy

Liquid resistivity

No active electronic

Low resolution, liquid dependent

String potentiometer

Potentiometer

Low power, no active electronic

Poor linearity, corrosion

Pressure

Silicon sensors

Inexpensive good resolution, wide

range measurements

Active electronic, need power

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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