SmartHardware
User Guide STR1000008X
10
How to calculate the values of R1 and R3
WITHOUT
120 ohm resistors at both
ends.
Example:
32 controllers and 5 V supply.
Each RS-485 node has a load impedance of 12K ohms. 32 nodes in parallel
give a total load of 375 ohms. In order to maintain at least 200 mV across 375
ohms we need a current of 0.53 mA. To generate this current from a 5V supply
requires a total resistance of 9375 ohms maximum. Since 375 ohms of this
total is in the receiver load, our bias resistors must add to 9K ohms or less.
Notice that very little bias current is required in systems without termination.
R1=R3=4.3K ohms.
Bias resistors can be placed anywhere in the network or can be split among
multiple nodes. The parallel combination of all bias resistors in a system must
be equal to or less than the calculated biasing requirements.
We produce these controllers. For your convenience we can solder
other resistors. We can leave blank the space and you can solder the
resistors that you need. Size is 1206.
3. Analog Inputs
Analog Input can withstand for a short time higher voltages. The only
limitation is heat over the resistance.
When an input is set in the current mode,
is a normal resistance of the input slightly to heat up.
v 2.1
V
in max = 40 V for T < 2sek
in both modes V/A
You can change input limit with
Rin
.
For example: 0 - 5V or 0 - 24V.
Analog Input X
V/A
Analog
Rin=100k
R=10k
R
s
h
=
5
00
GND