|
4
Channel A-D (OWAD4)
Description:
- This 1-wire card uses the
DS2450 IC and can measure four separate single ended analog
voltage input channels in the range of 0-2.55 or 0-5.10 volts.
- Each input has a 249 ohm resistor
to common for converting 0-20mA analog current to 0-4.98V.
- For digital input operation
a dry contact can connect +5V to an input. You can also drive
an input with a digital voltage as long as it does not exceed
5.1V.
- For higher input impedance
you may remove the 249 ohm resistors if not measuring 0-20mA
current.
Card Type:
Type |
Description |
1 |
Input Range 0-5.10V (Use
for 4-20 mA current and digital inputs) |
4 |
Input Range 0-2.55V (Alternate
voltage input range) |
Connector CN2
Pinout:
Pin
Numbers |
Description |
1 |
Jumper selectable
for Common or +5V |
2 |
A-D channel 4 |
3 |
A-D channel 3 |
4 |
A-D channel 2 |
5 |
A-D channel 1 |
6 |
Jumper selectable
for Common or +5V |
OWconfig:
The "Type" must be 1 or 4 as described
above. The "Mode" must always be "Separate power".
Modbus Register
Information:
This device has four consecutive
Modbus input registers, one for each A-D channel. The conversion
from Modbus register value (R) to volts (V) or current in mA
(C) is:
Type |
Voltage Range |
Modbus Range |
Conversion |
4 |
0-2.55V |
0-1023 |
V=R/400 |
1 |
0-5.10V |
0-1023 |
V=R/200 C=R*0.002002 |
The raw modbus reading is offset
by about 10 counts in the A-D converter. Therefore the range is
actually about 10 to 1023. For higher accuracy measurements you
should take this offset into account by calibrating with two known
input values at the low and high end of your range and calculating
conversion coefficients to do an exact calibration from raw counts
to required engineering units.
Specifications:
Parameter |
Specification |
Temperature |
-40 to +85C (-40 to +185F) |
Input Impedance |
249 ohm or about 1.0M ohm
if resistor is removed |
Power |
0.5 mA |
Resolution |
10 Bits |
Accuracy |
8 Bits |
Schematic
and Parts List:
Reference |
Part Number |
CN1 |
Digikey 281-1451-ND |
CN2 |
Digikey 281-1452-ND |
D1 |
Dallas Semi DS9503P |
D2-D6 |
Digikey SA5V0ADICT-ND |
U1 |
Dallas Semi DS2450S |
R1-R4 |
Digikey 249KQBK-ND |
|