EDI 242L Manuel d'utilisation - Page 5

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The Model 242L operating voltage is generated by a high efficiency isolated switching power supply.

The resulting bias voltage supplied to the Input circuits is electrically isolated from both 24VDC Logic

Ground and AC Line Neutral. The VDD supply for the microcontroller and display elements results from

a post regulated 5 Vdc.

1.5.2 INPUT CIRCUIT

Resistors R21, R7, R8, R25, and R19 (R22, R9, R3, R26, and R20) provide the input bias and voltage

scaling circuit. The resulting voltage at U20.3 (U20.4) is then processed by the microcontroller U20.

Gas tube CR2 (CR3) and diode CR 14 (CR16) provides input electrical transient protection.

1.5.3 MCU CIRCUIT

The microcontroller U20 processes the input voltages to perform the voltage threshold and pulse width

filtering functions. All signal processing is performed in the digital domain and controlled by firmware

embedded in the microcontroller. This unit does not rely on analog delay, pulse, or comparator circuits

for processing the input signals.

1.5.4 OUTPUT CIRCUIT

The output driver Q7 (Q8) is isolated from both the AC Mains and the internal GND reference of the

Model 242L by opto-couplers U8 (U9). CR9 (CR6) provides electrical transient protection for the output

driver Q7 (Q8).

1.5.5 DISPLAY AND SWITCH CIRCUIT

The LED indicator DS1 (DS3) for the channel output is driven directly from the microcontroller U20. The

input TEST switch SW1 (SW3) can be used to force the input state to the active status.

1.5.6 POWER SUPPLY CIRCUIT

The main power supply is a fully isolated switching design. The cabinet 24VDC input voltage is used to

drive switching controller U18. The transformer T1 is used by controller U18 to generate the isolated

and regulated 19 VDC input bias voltage VCC that drives the input circuits. The opto-coupler U21 and

reference U25 provide the closed loop feedback to the power supply controller U18 for regulation.

A second regulator U26 generates the 5.0 Vdc internal supply voltage VDD used by the processor

circuit from the 19 VDC bias. Inductor L2, C29, C31, and C24 filter the regulator U26 output to provide

clean VDD to the processor.

1.6 MAINTENANCE

The Model 242L requires no adjustments or preventive maintenance.

1.6.1 TROUBLE ANALYSIS

The following list should be used to trouble-shoot the Model 242L installation. If the Model 242L unit

itself is suspect, see Section 1.6.2 for a complete internal testing sequence.

a. Neither channel responds to DC inputs

a. Power supply fault

The Model 242L requires a nominal 24 Vdc input voltage. The unit will operate at voltages as

low as 10.8 Vdc, however, an input voltage below this may result in the unit entering a reset

state. In this case, the unit will appear to be non-functional.

b. Channel does not detect all inputs

Eberle Design Inc.

Model 242L Operations Manual

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