Section 13: Model 3750 multifunction control card
Series 3700A Switch and Control Cards Reference Manual
13-10
3700AS-909-01 Rev. B / December 2011
Analog output
There are two channels of isolated analog outputs on the Model 3750 card. Each channel can be
configured for either voltage output or current output. Voltage output provides for +/- 12 V and is
capable of providing up to 20 mA of current. Current output can be either 0-20 mA or 4-20 mA. The
voltage outputs also support programming of up to 1% over the full scale range. This can be used to
compensate for constant voltage drops in the system and cabling.
Each channel has its own separate common return line that provides the reference point for the
output. These lines are labeled as “VCOM” for the voltage output and “ICOM” for the current output. If
the outputs are to be referenced to some other point such as earth ground, the respective common
return signals must be connected appropriately.
Each output is connected through an onboard output relay. Both the output signal and its
corresponding return are connected at the same time that the output becomes enabled. Disabling the
output opens this output relay.
The following examples use the first analog output channel of a card in Slot 1, so the nomenclature
for the channel is
'1010'
.
Configuring the card for output type
The analog output channels default to voltage outputs. To configure them as current outputs:
channel.setmode('1010', channel.MODE_CURRENT_1)
NOTE
MODE_CURRENT_1 specifies 0-20 mA and MODE_CURRENT_2 specifies 4-20 mA.
To reconfigure the analog output as a voltage output:
channel.setmode('1010', channel.MODE_VOLTAGE_1)
NOTE
The analog output channels can only operate in one mode at a time. Specify either voltage output or
current output.
The outputs default to being disabled. To enable them:
channel.setoutputenable('1010', channel.ON)
Once the channel is enabled, any values written to the channel are seen on the output pins. To
disable the outputs:
channel.setoutputenable('1010', channel.OFF)
