Omega Vehicle Security OMP-MODL manual Application Notes DC Current Channels Channel Isolation

3... INTERFACE MODULES

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.

USING THE OMP-MODL 3-29