Vaisala PTB200 User Manual
PTB 200 1 (28)
Digital Barometers
SSD/Operating Manual 24th February 1993 PTB200-O0284-1.1
PTB 200 DIGITAL BAROMETERS
1 PRODUCT DESCRIPTION 2
2 INSTALLATION 3
2.1 Mounting 3
2.2 Grounding 4
2.3 Power connections 5
2.4 Serial output mode connections 6
2.5 Pulse output mode connections 7
2.6 Pressure connections 8
2.7 Multiple barometers on one RS 232C bus 9
3 SERIAL COMMANDS 10
3.1 General 10
3.2 Configuration commands 11
3.3 Operating commands 19
4 ADJUSTMENT AND CALIBRATION 22
4.1 Offset and gain adjustment 23
4.2 Multipoint adjustment 24
5 TECHNICAL DATA 26
Appendix 1 Commands
PTB200 Digital Barometer
SERIAL COMMANDS
Function Command Comment
serial bus settings SERI
echo on/off ECHO
output format FORM
pressure resolution FORM
units UNIT
integration time MTIM, FILT
settling time/response time MTIM, FILT
sending mode SMODE STOP, RUN and POLL modes
address ADDR for POLL mode only
defining single output
command
sleep mode SLEEP
list of software settings ?
SCOM in STOP and RUN modes
only
Appendix 1
starting output R
stopping output S
output single reading SEND in POLL mode address
required
setting output interval INTV
control of a single barometer
OPEN ,CLOSE
in POLL mode
resetting RESET
error messages ERRS
linear pressure adjustment LP
multipoint correction MPC, MPCI
1994-08-16 1
PTB 200 2 (28)
Digital Barometers
SSD/Operating Manual 24th February 1993 PTB200-O0284-1.1
1 PRODUCT DESCRIPTION
The PTB 200 A and PTB 201 A are fully compensated digital barometers designed to operate over a wide pressure and temperature range.
The final factory adjustment and calibration of the PTB 200 A is done
against a deadweight tester for best accuracy and pressure traceability.
The PTB 201 A is adjusted and calibrated by using electronic working
standards to meet the requirements of demanding weather station
applications. The PTB 200 digital barometers can also be readjusted by
the user with a local primary standard at up to eight selectable pressure
levels.
There are three available outputs in the PTB 200 digital barometers.
The RS 232C full duplex serial interface with software selectable serial
bus settings and pressure units is the standard output for connection
with computers. The user can also choose a TTL level bidirectional
serial output. For simple data logger use the pulse output can be
selected. The serial output of the PTB 200 barometers can be used in
continuous, interval or on-demand modes. The pulse output is activated
by an external trigger signal.
The PTB 200 digital barometers have two built-in features to reduce
power consumption; the user can choose a software controlled sleep
mode or use an external trigger signal to shut down the barometer.
The user can define various settings, such as integration time, settling
time and pressure resolution according to his application (see chapters
General and Configuration commands). The factory settings have been
chosen so that both a fast settling time and high resolution are
achieved. In applications where fast settling time is not required, we
recommend longer integration times to suppress noise effects such as
wind turbulance.
The PTB 200 digital barometers use Vaisala’s BAROCAP silicon
capacitive absolute pressure sensor. The BAROCAP pressure sensor
has excellent hysteresis and repeatability characteristics and very good
temperature and long-term stability. The ruggedness of the BAROCAP
sensor is outstanding.
From April 1993, the PTB 200 digital barometers are traceable to NIST
in the USA. Until March 1993 the barometers have been traceable to
L.N.E. in France.
PTB 200 3 (28)
Digital Barometers
SSD/Operating Manual 24th February 1993 PTB200-O0284-1.1
2 INSTALLATION
2.1 Mounting
The dimensions and recommended mounting positions of the PTB 200
barometers are shown in Figure 1.
145 (5.71)
133 (5.24)
120 (4.72)
Ø 6.5 (0.26)
65 (2.56)
104 (4.09)
120 (4.72)
139.5 (5.49)
27.5 (1.08)
Fig. 1 Dimensions and mounting of PTB 200 barometers
See Chapter 2.2 Grounding and 2.6 Pressure connection for further
information on electrical grounding and pressure connection
alternatives.
PTB 200 4 (28)
Digital Barometers
SSD/Operating Manual 24th February 1993 PTB200-O0284-1.1
2.2 Grounding
A single electrical cable with a screen and five or six wires is
recommended for power and serial bus connections. The cable
diameter should be 5 ... 10 mm.
The screen of the electrical cable must be grounded properly to achieve
best possible EMC performance. First remove the bushing from the
barometer housing and then push the cable through the bushing and its
brass disks. Expose the screen braid, but be careful not to open the
braid. Cut the braid and the wires to a suitable length. Pull back the
braid and press it between the two brass disks of the cable bushing to
make a full 360 degrees grounding (see Fig. 2). Then tighten the cable
bushing to the barometer housing.
CABLE SCREEN
BRASS DISKS
Fig. 2 Grounding the cable screening between the two brass disks of
the cable bushing
In addition to grounding the cable screen in the cable bushing, either
the barometer housing or the host end of the cable screen must be
grounded. To ground the barometer housing use one serrated lock
washer between a mounting screw and the housing; the lock washer
breaks the painting of the housing. When the host end of the cable
screen is grounded, the barometer housing must be mounted on an
insulating support to avoid grounding at two points.
PTB 200 5 (28)
POWER JUMPER
ON
OFF
-
CTRL
+
normal use
external control
using CTRL line
Digital Barometers
SSD/Operating Manual 24th February 1993 PTB200-O0284-1.1
2.3 Power connections
Two wires, one for supply voltage and another for supply ground, are
needed to connect power to the barometer (see Fig. 3).
Fig. 3 Power connections and jumpers
However, when a logic output is available in the host system, a third
wire can be connected to the power control terminal CTRL to enable
external control of the barometer. The POWER jumper of the barometer
must then be removed (see Fig. 3). The logic high TTL level (5 VDC)
turns the barometer on and logic LOW (0 VDC) turns it off. The CTRL
line can withstand higher logic voltage levels and is protected against
electric discharges. To return to normal operation simply re-insert the
POWER jumper.
PTB 200 6 (28)
GND
RX
TX
RS 232C TTL TTL INVERT
Digital Barometers
SSD/Operating Manual 24th February 1993 PTB200-O0284-1.1
2.4 Serial output mode connections
The serial communication can take place either using RS 232C or TTL
level signals. In both cases the barometer is connected to the host
system with three wires (TX, GND, RX) (see Figure 4). No handshaking
lines are used.
Fig. 4 Serial bus connections and jumpers
The selection between the RS 232C and TTL level output signals is
made with a jumper (see Fig. 4). The TTL level output signal has two
phase alternatives: TTL and TTL INVERT. The TTL output is in phase
with the TXD line of the Intel 8051 microprocessor and the TTL INVERT
output is in phase with the RS 232C output.
Although the PTB 200 barometers use a single polarity supply, both
positive and negative voltage levels occur in the output in the RS 232C
output mode. The higher the supply voltage, the higher are the output
voltages in the transmission line of the barometer; for example, at 12
VDC supply voltage the output voltage levels are approximately ± 8
VDC. The TTL level output voltages are 0 and 5 VDC.
If the supply voltage is raised and the baud rate lowered, the RS 232C
interface can be used over far longer distances than specified for the
standard RS 232C interface.
The receiving RX line accepts both RS 232C and TTL level voltages as
input; the TTL level phase selection does not affect the receiving line of
the barometer.
PTB 200 7 (28)
SERIAL OUTPUT
MODE SELECT
PULSE OUTPUT
MODE SELECT
LEDS
GND
PULSE TRIG
PULSE
RS 232C TTL TTL INVERT
PUSH BUTTONS:
Digital Barometers
SSD/Operating Manual 24th February 1993 PTB200-O0284-1.1
2.5 Pulse output mode connections (software version 1.05 or higher)
The pulse output mode uses the same terminals as the serial output
mode (see Figure 5). The transmitting terminal sends the pulse output
(TX/PULSE) and the receiving terminal of the barometer receives the
positive trigger signal (RX/PULSE TRIG).
Fig. 5 Pulse output connections, jumpers and push buttons
The pulse output mode must be separately selected. Two push buttons
(Fig. 5), arrow up and arrow down, are used to switch between the
pulse output mode and the serial output mode.
To select the PULSE OUTPUT operation mode:
1. Set the baud rate to 9600 (see SERI command).
2. Switch power off.
3. Press and keep down the arrow down push button.
4. Switch power on; the four LEDs go on and go out.
5. Release the push button; the LEDs go on and go out again.
To select the SERIAL OUTPUT operation mode:
1. Switch power off.
2. Press and keep down the arrow up push button.
3. Switch power on; the four LEDs go on and go out.
4. Release the push button; the LEDs go on and go out again.
5. Check the serial bus settings (see SERI command).
PTB 200 8 (28)
Digital Barometers
SSD/Operating Manual 24th February 1993 PTB200-O0284-1.1
The pulse frequency is about 4.5 kHz at baud rate 9600. The pulse
output is triggered using a positive pulse (e.g. 100 ms/5 VDC). The
pulse output voltage levels can be either RS 232C levels or TTL levels.
The selection is made with a jumper (Fig. 5).
The pressure resolution is limited in the pulse output mode to 0.1 hPa.
Each pulse represents 0.1 hPa, e.g. 10000 pulses equal 1000.0 hPa.
2.6 Pressure connections
The barometer is equipped with a standard Clippard barbed pressure
fitting with 10-32 external thread installed in the barometer. This fitting
is ideal for an 1/8" internal diameter tubing.
If some other pressure fitting needs to be used, it is possible to replace
the barbed fitting. The pressure connection in the barometer housing
has a metric M5 internal thread which is in practice compatible with
non-metric 10-32 internal thread.
The barbed pressure fitting is not recommended for turbulent or high
speed static wind conditions: the accuracy quoted for the PTB 200
digital barometers does not include any wind effects.
The PTB 200 barometers are designed to measure the pressure of
clean, non-condensating, non-conducting and non-corrosive gases
only.
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