Aim TTi LD300 Fonctionnement page 13

Remote Control Input
The CONTROL VOLTAGE terminals are used in two operating modes of the instrument (as
selected by the front panel LEVEL CONTROL switch):
In EXTERNAL VOLTAGE mode an analogue signal applied here sets the level of the load;
the scaling is 4 Volts full scale.
In EXTERNAL TTL mode, a logic signal applied here selects either the LEVEL A setting
(logic low) or the LEVEL B setting (logic high). The switching threshold is nominally +1·5V.
These terminals will tolerate a common mode voltage of up to ±100 Volts relative to
the negative terminal of the load input. The input impedance is 400kΩ from each
terminal to the load negative, so a common mode current will flow.
External Voltage Sense Input
To avoid errors in sensing the voltage of the source caused by voltage drops in the high current
wiring, connect the EXTERNAL SENSE terminals to the external circuit at the point where the
voltage needs to be measured (normally at the output terminals of the source under test). Move
the VOLTAGE SENSE SELECT slide switch to the EXT position.
Ensure that the source is connected with the correct polarity.
These terminals must not be connected to any voltage other than the source that is
connected to the load input.
Remote Disable Input
Apply +3V to +5V to the DISABLE INPUT terminals to disable the load input; they are the input to
an opto-coupler and are galvanically isolated from all other terminals. The input current is less
than 2·5mA at 5V. The INPUT ENABLE switch on the front panel must also be depressed for the
unit to operate.
Oscillator Sync Output
The SYNC OUTPUT is an open collector output of an opto-coupler driven by the signal from the
internal oscillator; it is galvanically isolated from all other terminals. A suitable pull-up resistor and
power supply (e.g. 4·7kΩ to +5V) are needed to generate a usable signal, which could be used
to trigger an oscilloscope. There is a 1kΩ series protection resistor.
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