123MB
Electrical
- Apr 25, 2008
- 265
Hi All
I am interested to know what you think an 'isolated Analog Input module is' as I have not been able to find a consensus on the meaning of this term among manufacturers and literature.
1) Some literature I have seen describes an isolated analog module as one where the analog common is isolated from power supply/chassis/earth ground.
2) However, most cheap analog input modules (i.e. 1769-IF8) are such that the analog common is isolated from power supply/earth/chassis ground, but these are not advertised as isolated analog input modules. On the 1769-IF8 there also appears to be isolation between each group of 4 channels, but there is no channel to channel isolation.
3) Alternatively some cheap analog input modules (i.e. Siemens 6ES7331-7KF02-0AB0) are advertised as an isolated module, however, as per the 1769-IF8 above, they only have power supply isolation and group isolation, no channel to channel isolation. Each group of 4 channels shares an ADC and hence there are common mode voltage restrictions.
So 2) and 3) above are both technically the same, electronically, but one is advertised as an isolated module and the other is not.
4) And then there's the high end Isolated Analog Input modules (i.e. 1769-IF4I) which have channel to channel isolation, and channel to power supply/chassis isolation, with a separate isolation amplifier and ADC per channel.
So what is an Isolated Analog Input Module?
Is an AI module isolated if the ACOM is isolated from power supply and chassis grounds? Surely this would include most AI modules
Or is an AI module isolated only if it has isolation between all channels, and to power supply/chassis? This would include only the top of the line expensive low density modules?
Thanks
Regards,
Michael.
I am interested to know what you think an 'isolated Analog Input module is' as I have not been able to find a consensus on the meaning of this term among manufacturers and literature.
1) Some literature I have seen describes an isolated analog module as one where the analog common is isolated from power supply/chassis/earth ground.
2) However, most cheap analog input modules (i.e. 1769-IF8) are such that the analog common is isolated from power supply/earth/chassis ground, but these are not advertised as isolated analog input modules. On the 1769-IF8 there also appears to be isolation between each group of 4 channels, but there is no channel to channel isolation.
3) Alternatively some cheap analog input modules (i.e. Siemens 6ES7331-7KF02-0AB0) are advertised as an isolated module, however, as per the 1769-IF8 above, they only have power supply isolation and group isolation, no channel to channel isolation. Each group of 4 channels shares an ADC and hence there are common mode voltage restrictions.
So 2) and 3) above are both technically the same, electronically, but one is advertised as an isolated module and the other is not.
4) And then there's the high end Isolated Analog Input modules (i.e. 1769-IF4I) which have channel to channel isolation, and channel to power supply/chassis isolation, with a separate isolation amplifier and ADC per channel.
So what is an Isolated Analog Input Module?
Is an AI module isolated if the ACOM is isolated from power supply and chassis grounds? Surely this would include most AI modules
Or is an AI module isolated only if it has isolation between all channels, and to power supply/chassis? This would include only the top of the line expensive low density modules?
Thanks
Regards,
Michael.