Board Components; Digital Circuitry - Mettler Toledo IND780 Guia De Instalacion

2.7.5.3.

Board Components

The flow meter board consists of digital circuitry, two isolated analog input circuits, and two open-
collector outputs with a 150mA, 5V power source.
2.7.5.3.1.

Digital Circuitry

The digital circuitry consists of a micro-controller, EEPROM and glue logic. The micro-controller
counts input pulses and measures flow rate for each isolated input circuit. It also does limit
comparisons on the inputs and sets the outputs based on the results. The EEPROM is used to store
configuration data that should not be lost at power-down. A USB version 1.0 communication links
the Flow Meter Option Board to the IND780 main controller board.
2.7.5.3.2. Isolated Analog Input Circuits
Each isolated input circuit consists of a comparator, an optocoupler, one set of hardware jumpers
and discrete resistors, capacitors, diodes, and a transient voltage suppressor. The comparator is
used to compare the input voltage to the switching voltage. Each input section has a hardware
jumper to select one of the four available input switching voltages. A second hardware jumper is
provided to enable or disable a 15 kHz analog filter on each input. The optocoupler isolates the
output of the comparator from the counter input of the microcontroller. The transient voltage
suppressor provides ESD protection for each input. The diodes provide over-voltage protection of
each input.
2.7.5.3.3. Open Collector Outputs
The output circuitry contains two non-isolated open collector 7407 drivers that can be used to drive
the input to an Opto 22 output module. The board also provides a 150 mA, 5V power source that can be used to provide power to an Opto 22 output module.
64057253 | 14 | 08/2014
Figure 2-71: Block Diagram, Channel 1 Shown
METTLER TOLEDO IND780 Installation Guide
2-45