Contemporary Control Systems BASremote User Manual (firmware 3.1.x) - Manual (Page 37)

TD040300-0MF
37
6.2 Input/Output Channels (I/O)
6.2.1 Universal I/Os
Six identical universal I/O channels allow any mix of inputs and outputs requiring only
two connections labelled A and B. Pin A is always more positive than pin B. Channels
are labelled I/O 1 through I/O 6 and are divided equally between two six-pin terminal
blocks. One terminal block is for I/O 1
–3 and the other is for I/O 4–6. Configuring is
done via the built-in web server. Input resolution is 10 bits; output resolution is 12 bits.
Schottky barrier diodes protect the electronics from over-voltage faults on inputs A and
B. Also, a PPTC (polymeric positive temperature coefficient) resettable fuse protects
terminal B from over-voltage when driven to ground.
Pin A can be an input or output. Pin B can be an input or ground. A D/A converter is
used for generating analog voltage or current outputs, and for providing excitation
current for contact closure sensing and for thermistor measurement.
In current output mode, pin B is grounded. The output burden applied to pins A and B
can range from 0 to 750
Ω. Since the internal burden is 250 Ω, the output voltage at pin
A can range from 0 –20 volts when driving 20 mA.
When measuring input voltages, pin A receives input while pin B is held at ground. Any
DC voltage in the range of 0
–5 V or 0–10 V can be measured.
When measuring current, pin B is unused and the input on pin A
sees a 250 Ω load.
To sense contact closure, 2 mA is output at pin A while pin B is grounded. Then the
voltage at pin A is measured. Any value below 0.3 volts (150
Ω) is considered a closed
circuit. Dry-contact or solid-state switches being sensed must withstand an open-
source voltage of 24 VDC and a current of 2 mA. For solid-state switches, the most
positive connection is at pin A and a saturation voltage under 0.3 V is required.
A 1 0 kΩ thermistor is applied between pins A and B. Thermistors are non-linear heat
sensing devices with a negative temperature coefficient of resistance. At nominal room
temperature (77 °F), the resistance of a Type II or Type III thermistor is 10 kΩ. Both
have curves with an accuracy of ±0.36 °F from 32 °F to 158 °F. Because higher
resistance thermistors (such as 10 k
Ω) introduce error due to the self-heating effect, lower
thermistor current is used — thus minimizing self-heat and measurement inaccuracy.
6.2.2 Relay Outputs
There are two independent SPDT relay outputs. For each output, both the NO and NC
contacts are brought out to a six-pin terminal block. Contacts are rated at 2A at 30 VAC
and 2A at 30 VDC. Wiring to the BAS Remote should only be Class 2. To control
higher voltages, the safer approach is to connect the coils of Class 2 interposing relays
to the contacts of the BAS Remote and have the contacts of the interposing relays
connect to the Class 1 circuits. These interposing relays should be further from the
BAS Remote and closer to the Class 1 equipment.