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Programming for the Synfi
The Synfi is a device which synchronizes sample data from two
identical Signal Acquisition Devices, which are connected to the SynFi
using fiber optical cables.
The concept of the Synfi is that it presents itself to the TMSi
driver as any other Signal Acquisition
Device, but connect two frontends simultaneously. Although we tried to
implement that concept to the fullest, some
small differences in behavior could not be
avoided.
Number of channels, channel names and channel ordering
The Synfi combines (and synchronizes) the outputs of two Signal Acquisition Devices. During that process, there are some rules regarding the order in which the Signal Acquisition Devices and the channel names are displayed.
The SynFi has 2 Fiber
ports, labeled “1” and “2”. The channel
names of the Signal Acquisition Device connected to port 1 are prefixed
by
“F1_”. So if the Signal Acquisition Device has a channel name “Exg1”,
the SynFi
shall list the name of that channel as “F1_Exg1”. The
channel names of the Signal Acquisition Device connected to port 2 are
prefixed
by “F2_”. So if the Signal Acquisition Device has a channel name
“Exg7”, the
SynFi shall list the name of that channel as “F2_Exg7”. The channel
order of
the Synfi is that first the channels of the Signal Acquisition Device
connected
to port 1 are shown, and then the channels of the Signal Acquisition
Device
connected to port 2 are shown.
The last channel of the Synfi carries the
sawtooth,
with channel name “/|/|/|”. The individual saw tooth channels of the
connected
Signal
Acquisition Devices are not displayed. The sawtooth of the SynFi is
created based upon the sawtooth of both connected Signal Acquisition
Devices.
If one or both of the Signal Acquisition Devices misses a sample, the
sawtooth of the Synfi will proportionally show this. Example: The slave
Signal Acquisition Device misses one sample. Then the sawtooth of the
SynFi will also miss a sample.
Some Signal Acquisition Devices have one channel in which the digi input is combined with the sawtooth. The Synfi then removes the sawtooth from that channel, and keep the digi input. As a result of that action, and due to technical reasons, the GetFrontEndInfo() will return a lower number of channels than the GetSignalFormat(). You should always use the number of channels from the GetSignalFormat().
The Digi channels of each Signal
Acquisition Device are the last shown channels for that Signal
Acquisition
Device.
It is possible that
applications of OEM's or customers re-order the channels in a way they
find useful. This is the
responsibility of the application itself, and should be described in
the manual of the application.
Common reference calculation
To get the
unmodified signal to the measuring application, the common reference
calculation should not performed by the driver when connecting the
Synfi. The reason is that the driver can not make a difference between
the channel sets of each frontend connected to the Synfi. So when using
the Synfi, turn of the reference calculation by using SetRefCalculation.
This means that the
Common Reference Derivation must be done in the application. To do
this,
we assume that the patient is connected as described in the Synfi
Manual, i.e. the patient ground is connected to the Signal Acquisition
Devices, and the Common Reference electrode is connected to channel 1
on both Signal Acquisition Devices. Channel 1 must be an EXG channel.
Because the signals coming from the Signal Acquisition Device are unprocessed, it is possible that signals show jumps in value when any other channels are switched off when signals on those channels are out of range. After the Common Reference Derivation is done, these jumps are removed.
For each received sample, for the Signal
Acquisition Device connected to port Fiber1, we subtract the value of
channel 1 (channel F1_EXG1) from all other EXG channels. Then for the
Signal Acquisition Device connected to port Fiber2, we subtract the
value of channel 1 (channel F2_EXG1) from all other EXG channels.
After the Common Reference Derivation is done, the resulting values for
all channels can
be used for any kind of mathematical operation.
To find out if a Synfi is connected, check the serial number in the FrontEndInfo structure. Each TMSi frontend has a 10 digit serial number, starting with a zero. The first 4 digits of the serial number of a Synfi are 0393. Because the serial number in the FrontEndInfo structure is an integer, the leading zero is not shown.
Impedance measurement
The impedance
measurement is done in two steps, assuming both Signal Acquisition
Devices
support
impedance measurement. Check the manuals of your Signal Acquisition
Devices to
see if they do.
During impedance measurement only one Signal Acquisition Devices is in
impedance mode,
and the other Signal Acquisition Device does not do anything. This is
for reasons of patient safety.
Keep in mind that
during impedance mode, the number of channels produced by the Synfi is
still the combined number of channels of both frontends. The sample
values of the channels of the frontend that is not in impedance mode
are set to zero.
The first time an impedance measurement is done using SetMeasuringMode with MEASURE_MODE_IMPEDANCE , the Signal Acquisition Device connected to port Fiber_1 is set in impedance mode, as can be seen by the switching on of the amber-colored LED’s on the front. The impedance measurement is stopped by using SetMeasuringMode with MEASURE_MODE_NORMAL, then the impedance mode of the Signal Acquisition Device connected to port Fiber_1 is turned off.
The second time a impedance measurement is done (using SetMeasuringMode with MEASURE_MODE_IMPEDANCE ), the impedance mode of the the Signal Acquisition Device connected to port Fiber_2 is set in impedance mode, as can be seen by the switching on of the amber-colored LED’s on the front plate. The impedance measurement is ended by using SetMeasuringMode with MEASURE_MODE_NORMAL, then the impedance mode of the Signal Acquisition Device connected to port Fiber_2 is turned off.
The third time a impedance
measurement
is done, the Signal Acquisition Device
connected to port Fiber_1 is set
in impedance mode again, and so on.
Set/Get the RTC clock
It is not possible to read out the RTC clock
or set the RTC clock of a single or both Signal Acquisition
Devices using the Synfi.
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