Ametek Thermox 2000 ATEX Series User Manual page 198

C-2 | Thermox Series 2000 WDG-HPII / HPIIC - ATEX
To determine the minimum external voltage supply required to power
the current outputs, use the following formula:
VEXTmin = .02 amps (RLoad + Rwires) + 4 volts
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
Skip this section if you don't measure combustibles.
NOTE
In addition, both of the combustibles current outputs have external
voltage options:
VEXT3+
VEXT3-
Jumper JP1 on the combustibles card allows you to define which power
source to use for current output 4. Jumper JP2 on the combustibles card
allows you to define which source to use to power current output 3. If
the jumper is in (factory default), the control unit uses its own power
supply to power the current output circuits. If you try to use an external
voltage at this time, the system will use whichever voltage is higher -
control unit voltage is normally about 28 volts. If the jumper is removed,
the external voltage source must be used to power the current output
circuits. The external voltage source must be 30 volts DC or less.
To determine the minimum external voltage supply required to power
these circuits, use the same formula as provided for the O2 current
output external voltage source described in the previous section. Modu-
lation can also be done in the same manner as IOUT1 or IOUT2.
VEXT4+
VEXT4-