Ametek Thermox Series 2000 WDG-IV User Manual page 187

C-2 | Thermox Series 2000 WDG-IV / IVC / IVCM
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 volt-
age 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. Modulation can
also be done in the same manner as IOUT1 or IOUT2.
VEXT4+
VEXT4-