Omega Vehicle Security OMP-MODL - Manual (Page 53)

3... I NTERFACE M ODULES
U SING THE OMP-MODL 3-29
interconnected within the logger and routed to the MLAD-1 Chassis Ground
terminal.
NOTE: Do not ground the signal wiring shield conductor at the sensor end
(the end away from the OMP-MODL) as this can induce additional noise into
the sensor wiring..
APPLICATION NOTES; DC Current Channels
Channel Isolation:
The negative terminal of MLIM-1 channels configured as DC Current
inputs are isolated from the OMP-MODL circuit ground by a 22Kohm
resistor (see Figure 3... -12).
Common Mode Input Range Considerations:
To prevent saturation of the input amplifier stages and erroneous
readings, no voltages should be applied to any input terminals that
are greater than 4.0V above or below OMP-MODL circuit ground.
In wiring multiple 4-20mA transmitters to the OMP-MODL through
an MLIM-1 channel, this 4.0V common mode level must not be
exceeded. Figure 3... -16 shows an acceptable method to connect
multiple transmitters running from a common power supply to
several channels on an MLIM-1 Interface Module channel without
exceeding this spec.
A simple method to comply with this spec is to insure that all
negative inputs (-) on channels configured as mA-LO inputs are
directly connected to the GROUND (-) terminal of the power supply
used for excitation of the 4 to 20 mA loop (eg the Omega
Engineering RPS-1, Rechargeable Power Supply). This will insure
that the voltage developed across the 100 ohm resistor internal to
the MLIM-1 mA-LO input channel will never exceed 2 VDC (ie 20mA
X 100 ohms = 2 VDC) relative to any channel’s (-) negative terminal.
In Figure 3... -16, the voltage developed between node [A] to [GND]
and node [B] to [GND] will never exceed 2VDC (in normal
operation).
Multiple Measurement Nodes on a Circuit:
When measuring different voltage points from a common circuit with
multiple channels (of one or more Interface Modules), measurement
errors from induced ground currents can exist. Single ended
measurements may be required. Consult the factory for application
assistance.
Input Overcurrent Fuses:
Each channel is protected by a 125mA fuse as shown in Figure 3... -12
(circuit) and Figure 3... -13 (physical location on module). This fuse will
protect the module from overcurrent surges received from malfunctioning or
improperly connected sensors and transmitters.