MPL115A datasheet(17/20 Pages) FREESCALE

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AN3956

Sensors

Freescale Semiconductor

Waterlevel Implementation with the MPXV5004G

The DEMOAPEXSENSOR has the MPXV5004G gauge pressure sensor on board. This is located on the backside of the demo

board. It has a top port, which is to be used with the supplied high temp silicone hose.

The output of the MPXV5004G is shown in Table 9.

The part has a offset of 1 V with a sensitivity of 9.8 mV/mm H20. On the DEMOAPEXSENSOR the value is sampled with a

12-bit ADC from the JM60 MCU. Note the following when considering waterlevel:

• It is important to implement Auto Zero (AN1636) to improve accuracy.

• Calibration can be done, ideally with a two point calibration.

• The sensor must be implemented with an air column buffer between the liquid and the sensor. This is done with a section

of tubing as in Figure 8.

• It is a gauge application, so the pressure measured is with respect to barometric pressure; when elevation varies, the

pressure seen at the sensor is the same, only dependent on liquid height.

Figure 8. Waterlevel Connection to Pressure Sensor

Figure 9. Hot Water Heater

Figure 10. Conical Bottom for Measurement

Table 9. Operating Characteristics (VS = 5.0 VDC, TA = 25°C unless otherwise noted, P1 > P2)

Characteristic

Symbol

Min

Typ

Max

Units

Pressure Range

POP

—

3.92

400

kPa

mm H2O

Supply Voltage

4.75

5.0

5.25

VDC

Supply Current

—

mAdc

Span @ 306 mm H2O (3 kPa)

Full Scale Span @ 400 mm H2O (3.92 kPa)

VFSS

—

3.0

4.0

—

Offset

VOFF

0.75

1.0

1.25

Sensitivity

V/P

—

1.0

—

V/kPa

Accuracy

0 to 100 mm H2O (10 to 60°C)

100 to 400 mm H2O (10 to 60°C)

0 to 400 mm H2O (10 to 60°C)

—

±1.5

±2.5

±6.25

%VFSS with auto zero

%VFSS without auto zero

Curved Bottom

Improved resolution when tank

is almost empty

More vertical height per

less volume H2O

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