through Channel 5 are transient protected and share a common return (GND) that is connected to the
chassis. Refer to
Layout for the location of P10.
The analog inputs are identified as Channel 0 through Channel 5. The first five, identified as
Channels 0 through 4, use range jumpers to select voltage or current mode. When set to voltage
mode, the analog inputs are single ended and measure up to 10V. When configured for current mode
a 250
Ω
current sense resistor will produce a 5V input at 20mA. See section
for information on setting the range.
The sixth analog input, identified as Channel 5, is configured for voltage mode only and measures up
to 32.768V. This input is typically used to monitor the input supply or battery voltage.
5.2.1
Analog Input 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
Ω
resistor built
into the 20mA input circuit. Self-powered transmitters have three terminals typically labeled
power
in
,
signal out
and
common
. Self-powered transmitters can have a current or voltage output. The
signal out
terminal 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 SCADAPack 350 VLOOP Supply that steps up the input voltage to
24V. The stepped up voltage is available on the Analog Connector P10 and is labeled VLOOP.
There is sufficient power available here for the five analog inputs and two analog outputs all
operating at 20mA. Significant power saving is possible by switching the Loop Supply off.
The second option is similar to the first except that the power supply is not stepped up to 24V. This
can be used with low voltage transmitters or when then the input voltage is sufficiently high that
further stepping up 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.
The third option is to power the transmitter from a power supply supplied by the user.
5.2.2
Analog Input Wiring Examples
Example wiring of several transmitters is illustrated in
•
Channel 0 has a loop powered current transmitter connected to VLOOP.
•
Channel 1 has a loop powered current transmitter connected to an external 24V power supply.
•
Channel 2 is unused.
•
Channel 3 has a self-powered voltage transmitter connected to an external 24V-power supply.
•
Channel 4 has a self-powered current transmitter connected to an external 24V-power supply.
•
Channel 5 is used to monitor the external 24V-power supply.
SCADAPack 350 Hardware Manual
February 14, 2007
17
