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System Operation
4.6
Signals I/O
The rear panel SIGNALS I/O connector provides several signals for remotely
controlling and monitoring the Model 6100 Laser Diode and Temperature
Controller.
There are four different grounds – the Chassis Ground, the Digital Ground, the
Laser Diode Analog Ground, and the Temperature Controller Analog Ground.
The Laser Diode Analog Ground, Temperature Controller Analog Ground,
and the Digital Ground are isolated from each other within the Model 6100.
The Chassis Ground is also isolated from the other three grounds. The
Chassis Ground and Digital Ground are available to the user on the back panel
DB-25 female connector. Although it is not required, these grounds may be
connected together externally provided ground loops are not introduced. Such
ground loops will degrade the performance of the unit. Because the USB
interface is referenced to digital ground, users should be especially careful not
to introduce a ground loop through an externally-connected computer, which
usually connect the Digital Ground to Chassis Ground.
The best approach is to have the chassis ground connected in one single point
in a system so that currents between the grounds are avoided.
4.6.1
Fault
The Fault signal is a TTL-Level output referenced to the unit's Digital
Ground. When a fault condition is detected, the unit will internally pull this
signal to about +5V using a 10 Kohm resistor. When a fault condition is not
detected, the unit will sink up to 8 mA to Digital Ground. For convenience,
digital ground is located at pin 14 of the same connector.
4.6.2
TTL Input
The TTL Input signal is a TTL-Level input referenced to the unit's Digital
Ground. The signal is internally pulled to about +5V via a 680 Ω resistor in
series with the photodiode of an optical isolator integrated circuit. This is a
general purpose input which can be monitored via software (see
TEC:TTL:IN? command) and used for internal/external event
synchronization. For convenience, digital ground is located at pin 15 of the
same connector.
Cables and wires connected to the Model 6100's SIGNALS I/O
connector must be fully shielded. The shield must be connected
to the shell of the mating connector. Failure to do so may
reduce the immunity of the Model 6100 to external electrical and
magnetic fields and thereby damage an attached laser diode.
CAUTION
67
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