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Operation
Altimeter Product Manual
0286-SOM-00001, Issue: 09
24
© Tritech International Ltd.
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In free running mode the unit will start to output data immediately upon power up (the data
rate is about 10Hz for a PA500 or 7Hz for a PA200). If the altimeter has been set to interrogate
mode it will not output data until the interrogate command (
Z
) is received, at which point a
single data string is transmitted to the surface computer.
In RS232 mode
When operating an RS232 altimeter it is possible to change the mode of
operation from free running to interrogate and back. Sending an
F
character will
change the unit to operate in free running mode and sending a
Z
character will
change it to operate in interrogate mode.
In RS485 mode
For RS485 units the mode should not be changed via serial commands. The
RS485 protocol used is a 2 wire half duplex and this means that the unit
never enters the 'listen' mode when set to free running so attempting to change
the unit with a serial command may result in unforeseeable results or loss of
communication with the device.
To confirm which mode the altimeter is in a simple test is to power on the unit and listen for
any audible clicks or pings. In free running mode the altimeter will start pinging as soon as it
receives power but in interrogated mode it should remain silent.
Warning
NEVER place the transducer close to the ear to listen for the clicks. Doing so
could result in permanent damage to the eardrum. Always remain at least 15cm
away from the transducer.
Data Stream Characteristics
The default altimeter output communication characteristics are as follows:
• 9600 baud
• 8 data bits
• 1 stop bit
• No parity
• No flow control
Depending on the dip switch settings the unit will either output a 0 result or the maximum
possible result whenever a valid signal is not detected (i.e., fail low or fail high). These settings
are, respectively,
Zero No Echo
(
ZNE
) or
Max No Echo
(
MNE
). These settings are fully
hardware controlled and cannot be over-ridden in software.