Bronkhorst FlowPlot - Manual (Page 6)

BRONKHORST ®
Device Control mode Description Situation
Digital meter
or controller
0 – Bus/RS232 Setpoint via bus or RS232 At normal communication with
fieldbus.
18 – RS232 Setpoint via bus or RS232, neglecting safe
state (for multibus instruments)
When no communicaton with
fieldbus, but only via RS232
Readout unit
(E-7000)
0 – Bus/RS232 Setpoint via bus or RS232 At normal communication with
fieldbus.
11 – Keyboard &
FLOW-BUS
Setpoint via E-7000 keyboard, bus or
RS232
At normal communication with
fieldbus.
Control mode 1 – Analog input means setpoint from analog input is active.
More detailed information about control modes can be found in document no. 9.17.023.
2.1.3 Realtime measurement
Realtime measurement will be only available in combination with the RS232/FLOW-BUS hardware interface. This
interface contains buffers and several extra processes for high speed data acquisition. When using realtime
measurement, up to four special processes in the interface will be programmed by FlowPlot. All data for the selected
parameters connected to a plot line will be collected by means of this interface. The interface collects the data and
adds time stamp information to it. While the PC may be temporarily busy, the interface will continue collecting data
and it will be less likely to miss important data. The graph may lag a little, but will contain more accurate information.
FlowPlot will detect automatically if this interface is connected and if realtime facilities can be used. Realtime
measurement is not available when a multibus instrument, connected via RS232, acts as the interface to the PC.
It is possible to disable realtime measurement manually. When realtime measurement is not available, the selection
box will be grayed and cannot be checked.
The Scantime can be changed in FlowPlot to set the sample time for data acquiring by the realtime processes in the
interface. This scantime is determined automatically based on the realtime poll time in FlowDDE and in most cases it is
not required to change it.
Using FlowDDE and FlowDDE2 simultaneously and at least one of them is using realtime measurement,
several timing issues may result in incorrectly synchronized plots for the different DDE servers. Plotting
from different DDE servers is advised to be used non-realtime only. FlowPlot will warn the user for this.
Additional information about poll times in FlowDDE and FlowPlot
The FlowDDE poll time is the default sample time for non-realtime processes, i.e. all normal polling actions. FlowDDE
will read the actual values from the instrument. Besides this, the poll time has influence on the speed FlowDDE (and
thus FlowPlot) sends setpoints and reads instrument parameter settings. Preferably don’t set this value too high (max.
500 ms). On the other hand, a value too low may slow down the overall bus system performance because too much
data is sent or requested via the bus.
The default poll time is 100 ms and is quite well for bus systems consisting of several instruments. For very small bus
systems (up to five instruments), the FlowDDE poll time can be set lower (to e.g. 75 ms or 50 ms) without slowing
down the bus system or the PC too much. For a single instrument connected via the RS232 interface on the
instrument, the poll time can be set even lower (to e.g. 25 ms) to achieve fast measurements.
In non-realtime mode FlowPlot will ask FlowDDE for actual values at the same interval as the poll time, unless the
sample time is manually set in FlowPlot. The Data acquisition time in the Options window determines how fast
FlowPlot samples values from FlowDDE (which is independent of the poll time in FlowDDE). In automatic mode, this
will be equal to the FlowDDE poll time.
The realtime poll time in FlowDDE is the sample time for FlowDDE to sample the realtime processes in the FLOW-
BUS/RS232 interface. It determines how often FlowDDE ‘looks’ into the interface to see if there are new samples. For
this, it is required that the interface has already read a value out of the instrument. Therefore it is needed that the
scantime in the interface module is at least equal, but better, lower than the realtime poll time in FlowDDE. Otherwise
the interface will frequently return no data. FlowPlot has an indicator Invalid data which will be lit in this case. If this
indicator is lit often, it is advised to change the settings for realtime poll time and scantime (i.e. higher the realtime
poll time or lower the scantime).
Page 6 FlowPlot 9.17.030