MODEL i330 PRODUCT SUMMARY
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The Model 330 Electrical Isolator provides 1000 Volts of optical isolation at one point within an instruNet network.  This is often used to eliminate ground loops between the computer and items under test, and to reduce noise that is transmitted from the computer to sensors.  When measuring small voltages (e.g. <10mV), optical isolation is sometimes critically important.  The Model 330 Electrical Isolator is very similar to the Model 300 Power Adaptor, described earlier, except for its isolation capability.  An external power source (e.g. #iNet-312.8) must be connected to the 5pin DIN Power Source Connector, to provide power to outbound devices.  Multiple Model 330's can be placed in one network (e.g. place one Model 330 every 4 Devices, in a 16 Device network). 

 
Fig 6.5 Model 330 Electrical Isolator Block Diagram

Fig 6.6  Example Application of Model 330 Electrical Isolator

Isolating From Earth Ground
The External Power Input pins 1 and 2 are both tied to the outbound instruNet device ground (case and pcb).  If this is also tied to the 3rd prong of the power supply AC input connector, and you want to isolate instruNet from this earth ground, then you would need to place a 2-to-3 prong Adaptor at the power supply input connector (or rip the 3rd prong out of the plug with a pair of strong pliers).

Wild Grounds
If the outbound devices are not seen by instruNet World, try temporarily holding a wire between the outer shell of the isolator inbound and outbound DB-25 connectors.  If the outbound devices are then seen by instruNet World (after Reset), then this indicates that a very high frequency exists between the two grounds and is causing problems.  The Model 330 is designed to sustain a signal between the two grounds that is 50V peak-to-peak with a 1000V/us slew rate (e.g. slews 1Volt in 1ns); and this is adequate is most applications.

Slower Speeds
Since the optical isolators introduce delays, the Model 330 reduces the speed of the instruNet network from 4M bits/sec to 1.33M bits/sec, on short networks.  In a worse case scenario, this would reduce the maximum sample rate 3 to 1.