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4.2.1 TDC Stop Inputs
The Octa Channel TDC provides 1x (R442, R443), 2x (R451) and 4x (R461) HDMI sockets (“TDC 1” - “TDC 4”)
for 16 (R442, R443), 8 (R451) and 4 (R461) signal inputs from the ACU. The TDC inputs are laid out for PECL
signal levels.
13. Power Switch to turn the TDC ON/OFF. Lighted, when set to ON (R442, R443, R451, R461)
Take care that measurements are performed either with the internal start signal (Ext_
Gpx_Start = 0 respectively = NO) and no signal applied to the TTL Start Input (BNC socket)
or with an external start signal (Ext_Gpx_Start = 1 respectively = YES) applied to the TTL
Start Input. In all other cases the TDC is not working correctly.
Note
4.2.2 TDC Start Input
An external start signal must be provided to the TDC for real time resolved measurements. The external
start signal must be applied as a LVTTL (minimum amplitude of at least +2.1V on 50Ohms) signal to the
“Start In” (BNC socket). The start signal must always be in 50Ohm technique as the “Start In” is terminated
with 50Ohms internally within the TDC. In addition the software must be set to accept external start signals,
by changing the corresponding entry in the tdc_gpx3.ini file.
The corresponding entry in the tdc_gpx3.ini file is:
Ext_Gpx_Start = X
X is either NO or YES.
The default setting is NO
.
“Ext_Gpx_Start” = YES must be set for the TDC to accept the external start signal.
In addition the following entries in the tdc_gpx3.ini must be set as follows:
StartCounter = YES
StartPeriod = 0x800000
Measurements are performed in respect to an internal start signal of the TDC when “Ext_Gpx_Start” =
NO. This internal start signal has no time correlation to any external clock and therefore also not to the
incoming stops. The internal start signal can be used for pure 2D(x, y) measurements. Any external start
signal must be disconnected from the start input of the TDC, when working with the internal start signal.
The rise time of the external start signal is of great importance, the faster the rise time, the better the time
resolution. The maximum frequency of the start pulse must not exceed 9MHz.
Note
Do not forget to save the ini file after any changes you make and restart the software. For
further information check the software manual.
Time-to-Digital-Converter Octa Channel TDC Manual | Surface Concept GmbH
