Instruction Manual

Introduction 25

EOS-4000

1.8.2 General Purpose Digital Input (EDI)

The EOS-4000 provides 32 opto-isolated digital input channels on

the front panel. Circuitry of the isolated input channel is as follows.

As shown, signal connections for a supply and load connected to

an isolated input, here in the EOS-4000, can determine when a

load is powered. The load is connected to the power supply by a

switch and can be any DC voltage between 12 and 24 VDC. When

the switch is open, no current flows through the load and no volt-

age is applied to the load or to the EOS-4000 DI channels.

The digital logic of the EOS-4000 then registers a logic high for the

channel. When the switch is closed, current flows through the

diode and the EOS-4000 registers logic low for the channel.

Reducing DI channel Forward Current for High Voltage

As input voltage exceeds 12 V, the input current drawn by the

EOS-4000 (forward current If) rises commensurately. At 24 V,

for example, current per line is determined by the formula:

(24V- 0.5V)/2.32k = 10.129 mA

To reduce the current and the power drawn, on a monitored cir-

cuit, for example, another resistor can be added in series with

the 2.32 kΩ current-limiting resistor, as shown.

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