Technical Description
Sealevel Systems
ISO-16
Page
6
The input impedance of each isolated input is 560 ohms (factory default, this
can be modified by user or at factory if requested). The opto-isolator requires
approximately 3 mA to turn on. The maximum input current is 60 mA. Two
points must be considered when selecting the input resistor. The first is turn on
voltage for the circuit to sense, and second is the maximum input voltage.
Maximum input voltage must not provide too much power to the input resistor,
and must also not overdrive the opto-isolator input current specification. The
following formulas apply:
Turn on current: 3 mA
Isolator diode drop: 1.1 V
Resistor power Max: .25 W
Turn on Voltage = diode drop + (turn on current) x (resistance)
Or :
1.1 + (.003) x R
Maximum voltage = square root of (.25 (resistor value))
The following table shows four common input resistors and the ranges
associated with each .
Input Resistor
(Ohms)
Value Turn-On
(Volts)
Max Input Range
(Volts)
Max Current
(mA)
220
1.76 to 7.4
2 to 6
29
560
2.8 to 11.8
3 to 12
19
1K
4.1 to 15.
8.4 to 16
15
2.2K
7.7 to 23.4
8 to 24
10
Increasing the input resistor accordingly can increase the maximum input
voltage. Because removable/replaceable DIP resistor networks are utilized,
they can easily be replaced with a different value. This can be done at the
factory, if necessary
. The input circuits are not designed for monitoring 120-volt
AC circuits and damage will occur if connected to a 120-volt AC circuit
.
