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.
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
0
—
3.92
400
kPa
mm H2O
Supply Voltage
Supply Current
VS
IS
4.75
—
5.0
—
5.25
10
VDC
mAdc
V
Span @ 306 mm H2O (3 kPa)
Full Scale Span @ 400 mm H2O (3.92 kPa)
VFSS
—
—
3.0
4.0
—
—
Offset
VOFF
V/P
0.75
—
1.0
1.0
1.25
—
V
Sensitivity
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 with auto zero
%VFSS without auto zero
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
Curved Bottom
Improved resolution when tank
is almost empty
More vertical height per
less volume H2O
Figure 9. Hot Water Heater
Figure 10. Conical Bottom for Measurement
AN3956
17
Sensors
Freescale Semiconductor
FREESCALE [ Freescale ]
