Vaisala | PMB100 | PMB100 Barometer Module

PMB100 Barometer Module
USER'S GUIDE
M010035en-A
September 2000
PUBLISHED BY
VAISALA Oyj
P.O.Box 26
FIN-00421 Helsinki
Phone(int.): (+358 9) 894 91
Telefax: (+358 9) 894 9227
Telex:
122832 vsala fi
Visit our internet pages at http://www.vaisala.com
©Vaisala 2000
No part of this manual may be reproduced in any form or by any
means, electronic or mechanical (including photocopying), nor may its
contents be communicated to a third party without prior written
permission of the copyright holder.
The contents of instruction manuals are subject to change without
prior notice.
CHAPTER 1_______________________________________________________ GENERAL INFORMATION
Table of contents
CHAPTER 1
GENERAL INFORMATION ............................................................................4
Safety .........................................................................................4
Warranty ....................................................................................4
CHAPTER 2
PRODUCT DESCRIPTION.............................................................................5
BAROCAP® pressure sensor..................................................5
CHAPTER 3
OPERATION ...................................................................................................7
Connections ..............................................................................7
Dimensions in mm (in inches).................................................9
Pressure calculations...............................................................9
Offset/Gain corrections..........................................................10
CHAPTER 4
TECHNICAL DATA.......................................................................................11
Specifications .........................................................................11
Operating range..............................................................11
Accuracy.........................................................................11
General...........................................................................11
APPENDIX A
READING COEFFICIENTS FROM THE EEPROM......................................13
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CHAPTER 1
GENERAL INFORMATION
Safety
Throughout the manual, important safety considerations are
highlighted as follows:
WARNING
Warning denotes a serious hazard. It calls attention to a procedure,
practice, condition or the like, which, if not correctly performed or
adhered to, could result in injury to or death of personnel.
CAUTION
Caution denotes a hazard. It calls attention to a procedure, practice,
condition or the like, which, if not correctly performed or adhered to,
could result in damage to or destruction of part or all of the product.
NOTE
Note highlights important information. It calls attention to an
essential procedure, practice, condition or the like.
Warranty
Vaisala issues a guarantee for the material and workmanship of this
product under normal operating conditions for one (1) year from the
date of delivery. Exceptional operating conditions, damage due to
careless handling and misapplication will void the guarantee.
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CHAPTER 2_______________________________________________________ PRODUCT DESCRIPTION
CHAPTER 2
PRODUCT DESCRIPTION
The PMB100 for OEM applications is a new circuit board mountable
barometric pressure transducer that is designed to interface with an
AD converter and a microprocessor.
The PMB100 module is characterized over 800 to 1100 hPa (mbar)
pressure range and over –5 to +45C temperature range. It ouputs
pressure dependant voltage within 0 and 2.5 VDC along with a
reference voltage of 2.5 VDC. All pressure and temperature related
coefficients are given in a module specific certificate and also stored
in an incorporated EEPROM, which uses the I2C interface. All the user
needs to do is to measure the temperature of the module and the two
voltage outputs and then calculate the compensated pressure reading
using the coefficients. A final offset correction against a high-class
pressure standard is recommended as a final touch.
BAROCAP® pressure sensor
The PMB100 barometer modules use the BAROCAP® silicon
capacitive absolute pressure sensor. The BAROCAP® sensor has
excellent hysteresis and repeatability characteristics, low temperature
dependence and a very good long-term stability. The ruggedness of
the BAROCAP® sensor is outstanding and the sensor is resistant to
mechanical and thermal shocks.
Silicon diaphragm
Thin film metallization
Silicon
Glass
Silicon
Vacuum gap
Figure 1
The BAROCAP® pressure sensor
The BAROCAP® pressure sensor consists of two layers of single
crystal silicon having a layer of glass between them. The thinner
silicon layer is etched on both sides to create an integrated vacuum
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reference chamber for the absolute pressure sensor and to form a
pressure sensitive silicon diaphragm. The thicker silicon layer is the
rigid base plate of the sensor and it is clad with a glass dielectric. The
thinner piece of silicon is electrostatically bonded to the glass surface
to form a strong and hermetic bond. Thin film metallization has been
deposited to form a capacitor electrode inside the vacuum reference
chamber; the other electrode is the pressure sensitive silicon
diaphragm.
The coefficients of thermal expansion of silicon and glass materials
used in the BAROCAP® pressure sensor are carefully matched
together in order to minimize the temperature dependence and to
maximize the long-term stability. The BAROCAP® pressure sensor is
designed to achieve zero temperature dependence at 1000 hPa and its
long-term stability has been maximized by thermal ageing at an
elevated temperature.
The BAROCAP® capacitive pressure sensor features a wide dynamic
range and no self-heating effect. The excellent hysteresis and
repeatability characteristics are based on the ideal spring
characteristics of single crystal silicon. In the BAROCAP® pressure
sensor, the silicon material is exerted to only few percent of its whole
elastic range.
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CHAPTER 3________________________________________________________________ OPERATION
CHAPTER 3
OPERATION
Connections
The pin assignments of the PMB100 module are according to Figure
2. Connect 8...16 VDC supply voltage (typically 2 mA) to the pin VDC
and the ground plane directly to the pin GND. The output signal (0...2.5
VDC) is measured from the pin OUT and the reference signal (2.5 VDC
± 2%) from the pin REF.
If the coefficients are read from the EEPROM, the pin +5 V, SCL and
SDA are also connected. The +5 V-pin is used for supply voltage of the
EEPROM. The pins SCL and SDA are for data transfer between the
EEPROM and a microprocessor.
Temperature of the module is measured with an external T sensor,
which should be placed as close to the module as possible.
The module can also be switched to shut down mode by using a TTL
level trigger on the pin SH. A signal 0.7 V or lower activates and a
signal higher than 2 V switches the module off.
REF
SH
Out
VDC
GND
+ 5V
SCL
SDA
Figure 2
Pin assignments
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In applications where adverse electromagnetic fields exist, an
additional EMI protection may be necessary. In Figure 3, there is an
example of an electromagnetic interference protection of the PMB100
module. The EMI filters should be placed as close to the pins as
possible.
GND directly connected
to ground plane
+
Power
regulator
filter
filter
PMB100 module
GND
VDC
OUT
REF
filter
Vout
Copper pour connected to ground.
Vref
Vout
VDC
GND
Vref
Figure 3
Electromagnetic interference protection of the
PMB100. Filters, for example, T-type EMI
suppression filters with capacitance of 47pF (like
Murata, DSS310-55Y5S470M100). This connection
setup fulfills the RF field immunity standard
EN61000-4-3.
8 ____________________________________________________________________ M010035EN-A
CHAPTER 3________________________________________________________________ OPERATION
Dimensions in mm (in inches)
Pressure calculations
Measure the following parameters of the PMB100 barometer module:
- output voltage Vout
- reference voltage Vref
- module temperature Tm (°C)
NOTE
External T-sensor is required for temperature compensation purpose
with minimum ±1°C accuracy.
1°C error in temperature measurement causes 0.14 hPa error in
pressure value.
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In pressure calculation, normalized voltage (Vn) and temperature (Tn)
are required. The normalization of the parameters is performed by
using the equations 1 and 2.
æ Vout ö
Vn = ç 2 ⋅
− 1, Vn ∈ [− 1...1]
è Vref
(1)
Tm
− T 0, Tn ∈ [− 1...1]
128
(2)
Tn =
Constant T0 is found in the list of coefficient or in the EEPROM.
Normalized pressure Pn is calculated according to the equation 3. All
the module specific coefficients are available in the list of coefficients
supplied with each module or in the EEPROM.
éa00 + a10 ⋅Vn + a 20 ⋅Vn 2 + a30 ⋅Vn 3
ù
ê
2
Pn = k ⋅ ê+ a01 ⋅ Tn + a02 ⋅ Tn
, Pn ∈ [− 1...1]
ê
2
2
3
êë+ a11 ⋅Vn ⋅ Tn + a12 ⋅Vn ⋅ Tn + a 21 ⋅Vn ⋅ Tn + a31 ⋅Vn ⋅ Tn
(3)
Compensated pressure P is then calculated by using the equation 4.
P = 150 ⋅ Pn + 950 hPa
(4)
Offset/Gain corrections
A final offset/gain correction against a high-class pressure standard is
recommended as a final touch. The offset and gain adjustments are
done after the pressure calculation by the user's host system.
10 ___________________________________________________________________ M010035EN-A
CHAPTER 4____________________________________________________________ TECHNICAL DATA
CHAPTER 4
TECHNICAL DATA
Specifications
Operating range
Pressure range (1 hPa = 1 mbar)
Temperature range
Humidity range
800 ... 1100 hPa
-5°C ... +45°C
< 80%RH
Accuracy
Linearity
Pressure hysteresis
Repeatability
Accuracy at +20°C
±0.25 hPa
±0.05 hPa
±0.05 hPa
±0.3 hPa
Temperature hysteresis
Accuracy (-5°C ... 45°C)
±0.3 hPa
±0.5 hPa
Total accuracy after the OFFSET correction (+20 °C, 1000 hPa)
performed by the user is obtained by using the following equation:
Total accuracy = ± 0.5 2 + n 2 hPa
(5)
where n is the calibration uncertainty
Without the OFFSET correction performed by the user:
Total accuracy (-5 ... +45 °C)±1.00 hPa
Long-term stability
Effect of thermal or mechanical
shocks
±0.20 hPa/year (typical)
<0.20 hPa
An error of 1 °C in temperature measurement causes an error of 0.14
hPa in pressure.
General
Supply voltage range
9...16 VDC
Shutdown control with TTL level trigger
<0.7 V
module ON
>2.0 V
module OFF
Supply voltage sensitivity
less than 0.1 hPa
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Current consumption
operation mode
shutdown mode
Output voltage
output
reference
Resolution
Load resistance
Load capacitance
Settling time at power-up
Response time
Warm-up shift
Pressure hose
Maximum pressure limit
Electrical connectors
Weight
2 mA (typical)
150 µA (typical)
0...2.5 V
2.5 V ±2% (type LM4431M3)
0.1 hPa
10 kΩ minimum
100 nF maximun
200 ms
100 ms
less than 0.05 hPa
1/16'' id 1/8'' OD, vinyl hose
300mm
2000 hPa
two 6-pin pin headers, 2.54 mm
grid
70 g
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APPENDIX A _______________________________________ READING COEFFICIENTS FROM THE EEPROM
APPENDIX A
READING COEFFICIENTS FROM THE
EEPROM
The PMB100 module has a Xicor's EEPROM memory, type X24C02,
which uses the I2C interface. All the pressure and temperature related
coefficients are stored in the memory in form of 32 bit, and can be
read by a microprocessor (see Table 1). The pin assignments are as
shown in Figure 2 on page 7. Detailed instructions of the EEPROM are
found on Xicor's web pages (http://www.xicor.com/).
NOTE
EEPROM can not be read if the shut down is active (ON).
Table 1
Name
Product code
Serial number
Calibration date
Scaling factor
Normalized room
temperature
Normalized coefficients
memory map
Type
Length
EEPROM
Symbol
PCode
Sno
Date
k
T0
8-bit int
32-bit int
[Bit]
8
32
24
8
32
a00
a10
a20
a30
a01
a02
a11
a21
a31
a12
32-bit int
32-bit int
32-bit int
32-bit int
32-bit int
32-bit int
32-bit int
32-bit int
32-bit int
32-bit int
32
32
32
32
32
32
32
32
32
32
8-bit int
Memory
address
[Byte]
0
1 - 4
5 - 7
8
10 - 13
Range
[0...256]
[-1...1]
14 - 17
18 21
22 25
26 29
30 33
34 37
38 41
42 45
46 49
50 53
[-1...1]
[-1...1]
[-1...1]
[-1...1]
[-1...1]
[-1...1]
[-1...1]
[-1...1]
[-1...1]
[-1...1]
[0...256]
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The form of coefficients (32-bit signed integer) in the eeprom:
eeprom:
MSB LSB
MSB LSB
MSB LSB
MSB LSB
byte_0 xxxxxxxx byte_1 xxxxxxxx byte_2 xxxxxxxx byte_3 xxxxxxxx
long_int: bit_31 xxxxxxxx bit_23 xxxxxxxx bit_15 xxxxxxxx bit_7
MSB
xxxxxxxx bit_0
LSB
32-bit signed integer → FLOAT (1.0...-1.0)
float=signed_long_int/2^31
In following there is an example of C-program to convert the 32 bit
coefficients to floating point numbers.
unsigned char read_eeprom(addr)
{
/* eeprom read routine */
return(read_data);
}
/*------------------------------------------------------------------------- -------------------*/
void read_long_int( char addr, long int *coef )
{
unsigned char *pointer=(char*)coef;
*pointer++=read_eeprom(addr++);
*pointer++=read_eeprom(addr++);
*pointer++=read_eeprom(addr++);
*pointer=read_eeprom(addr);
}
/*------------------------------------------------------------------------- -------------------*/
void main(void)
{
long int long_coef=0;
(32 bit) */
float float_coef=0.;
/* signed long integer
read_long_int(14,&long_coef);
float_coef=(float)long_coef/0x80000000;
printf("Float is %e\r\n",float_coef);
}
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