ADLINK EOS-4000 - Manual (Page 37)

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)/2.32kΩ = 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.
DICOMn
DIn
Ri