5604 Input/Output (I/O) Module - Hardware Manual
October 19, 2007
5.3 Wiring
The analog inputs support loop powered and self powered transmitters. Loop powered transmitters
are two terminal devices that connect between a power supply and the analog input. The loop
current continues from the power supply, through the transmitter and to ground through a 250
resistor built into the 20mA input circuit. Self-powered transmitters have three terminals called
power in, signal out and common. Self-powered transmitters can have a current or voltage output.
The signal out connects to the Analog Input Channel, the common connects to GND and the power
in connects to a power supply.
There are three options for the user when selecting the power source. In all cases it is important for
the user to ensure that the transmitter has enough voltage for proper operation. The transmitter
manufacturer supplies the minimum operating voltage specification of the transmitter. The analog
input requires a minimum of 5V.
The first option is to use the 5604 I/O Module VLOOP Supply that boosts the input voltage to 24V
with a 12V to 24V DC/DC converter. The stepped up voltage is available on connector P3 and is
labeled VLOOP. There is sufficient power available for the eight analog inputs and four analog
outputs all operating at 20mA. Significant power saving is possible by switching the VLOOP supply
off when measurements are not being made.
The second option is similar to the first except that the power supply is not boosted up to 24V. This
can be used with low voltage transmitters or when the input voltage is sufficiently high that further
boosting is not necessary. It is still possible to switch the supply off under program control. When
the step up is turned off, VLOOP is approximately 0.5V less that the power input voltage.
5.3.1 Wiring Examples
Several wiring examples for loop and self powered transmitters are illustrated in Figure 8: Analog
Input Wiring. The transmitters are wired as follows:
Channel 0 has a loop powered current transmitter connected to VLOOP.
Channel 1 has a self-powered voltage transmitter connected to the external power supply.
Channels 2 through 6 are unused.
Channel 7 has a self-powered current transmitter connected to the external power supply.
Channel 8 is used to monitor the external power supply.
If a 12V external power supply or battery is used the application can boost this voltage to 24V at
VLOOP using the internal DC/DC converter. If a 24V external power supply is used it is
unnecessary to boost this voltage.
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