1B22
Synchronizing Multiple 1B22s: In applications where mul-
tiple 1B22s are used in close proximity, radiated individual
oscillator frequencies may cause “beat frequency” related out-
put errors. These errors can be eliminated by driving the SYNC
pins of all the units with a 40 kHz clock circuit at 50% duty
cycle (Figure 5). The SYNC input typically has an input imped-
ance of 150 kΩʈ180 pF.
APPLICATIONS
Isolated D/A Converter: The 1B22 offers total ground isola-
tion and protection from high voltage transients in interfacing
D/A converters to standard 4 to 20 mA current loops. The D/A
converter, such as the Analog Devices’ 12-bit AD7245
DACPORT®, should be connected for operation on the unipo-
lar 0 V to +10 V output range. This is shown in Figure 7.
Figure 5. Multiple 1B22s’ Synchronization
Figure 7. D/A Converter–Isolated 4-20 mA Interface
Loop Supply Requirements: The 1B22 design allows flexible
loop supply options. The loop supply voltage required for any
value of load resistance can be calculated from the following
equation:
Pressure Transmitter: In Figure 8, the 1B22 is used in a
pressure transmitter application to provide complete input-
output isolation and avoid signal errors due to ground loop cur-
rents. The process pressure is monitored with a strain gage type
pressure transducer interfaced by the Analog Devices’ 1B32
transducer signal conditioner. The high level voltage output of
the 1B32 is converted to the isolated 4 to 20 mA current for
transmission to a remote recorder or indicator.
2RL +780
VLOOP
=
106
This value allows for approximately 10% overrange capability.
The graph in Figure 6 shows the relationship between supply
voltage and load resistance.
Figure 8. Isolated Pressure Transmitter
Figure 6. Loop Supply vs. Load
DACPORT is a registered trademark of Analog Devices, Inc.
–4–
REV. B
ADI [ ADI ]
