C-2 | Thermox TM2000 Oxygen Analyzer
To determine the minimum external voltage supply required to power the
current outputs, use the following formula:
VEXTmin = .02 amps (RLoad + Rwires) + 4 volt
where:
VEXTmin = the minimum external voltage required to power current
output circuit
RLoad = the load resistance of the current output device
Rwires = the resistance of the wires
Modulation of External Power Loop Using Current Outputs
Figure C-1 shows an example of the connection method when you want
to produce a modulated current loop from an external power supply and
a load device. All current output channels (IOUT1 and IOUT2) can be
connected as shown in Figure C-1.
IOUT1 and IOUT2 must share the same power supply if both of these
channels are used, or two power supplies can be “ORed” together using
a diode from each power supply positive terminal (diode anode to power
supply) to the VEXT1,2+ terminal. The power supply minuses would be
tied together and connected to one side of the both loads. The other side
of one of the loads would be connected to IOUT1+ terminal, and the
other side of the other load would be connected to the IOUT2+ terminal.
For each current output channel used in a current loop modulation ap-
plication, the jumpers should be removed for that channel.
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