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Parenthesis denote a value that must be filled in by the user. For
example,
(unit ID)<CR>
should be changed to
A<CR>
when using a
device with Unit ID “A”. It may also be useful to note that commands are case
insensitive. For example,
A<CR>
is equivalent to
a<CR>
.
Polling Mode
All Alicat devices are sent in Polling Mode with Unit ID A unless otherwise
requested. Polling a device will return a data frame of the current
measurements in the device in units shown on the display. See Data Format,
later in this section, for more information. Each unit may be polled individually
using the command
(unit ID)<CR>
.
A device’s Unit ID may be changed using the command
(current unit
ID)@=(desired unit ID)<CR>
. The Unit ID can also be changed via
the front panel using the RS-232 / RS-485 communication select menu. Care
should be taken not to assign the same unit ID to more than one device on a
single COM port. Up to 26 units may be connected simultaneously as Unit IDs
between A and Z are allowed.
Streaming Mode (RS-485 units do not have streaming mode)
In Streaming Mode, a device will automatically output the data stream at a
pre-determined rate. The default rate is set to 50 ms and can be changed via
register values for units with software version 4v30 or newer. Only one unit on
a given COM port may be in streaming mode at a time.
To change a unit from Polling Mode to Streaming Mode, type
(unit
ID)@=@<CR>
. This is equivalent to changing the unit ID to “@”. If data does
not appear, check all the connections and COM port settings.
When sending a command to a unit in streaming mode, the flow of information
will not stop while the user is typing; and the typed text may not be readable
depending on the terminal settings. If the unit does not receive a valid
command, it will ignore it. If in doubt, simply perform another carriage return
and start again.
To change a unit from Streaming Mode to Polling Mode, type
@@=(unit
ID)<CR>
. If entered correctly, the data stream will stop and the device will
now be in polling mode.
Data Format
The data frame represents the current measurements in the device in the
“device units” selected on the unit. By default, mass flow controllers are
configured to output seven columns of data.
Devices come standard with units of PSIA, °C, and either SLPM/LPM or SCCM/
CCM, depending on the flow range of the device. Note that the “button units”
available on portable units will not affect the serial output. The first column
is the unit ID. This column will be excluded if the device is in streaming mode.
The next columns are absolute pressure, temperature, volumetric flow rate,
mass flow rate, setpoint value, and selected gas, respectively.
