SM1231 maximum destruction current / lightning protection

Hi all

With an SM1231 AI card there appears to be a maximum current per input of 40mA, the datasheet describes this as "permissible input current input (destruction limit), max".

Firstly, to confirm, does that mean if 40mA is exceeded on any input will that input fail? If so presumably we need to protect each input with a fast fast acting fuse under 40mA?

We have a site that is prone to lighting strikes, which would happen in the 4-20mA sensor inputs. Does anyone know of any 4-20mA current loop surge protectors that limit the output to under the 40mA "Destruction Limit" of 40mA?

Thanks for your help

Arun

arunrf

To give a bit more background - the 4-20mA sensors are about 1km from the AI card in a river, so we can get surges from lightning strikes coming through the ground to cables or water to the sensors themselves.....

 1km is too much distance between the sensor and the input.

Hati

 

arunrf

To give a bit more background - the 4-20mA sensors are about 1km from the AI card in a river, so we can get surges from lightning strikes coming through the ground to cables or water to the sensors themselves.....

 1km is too much distance between the sensor and the input.

We have no choice, it is a hydropower system, we need to measure the water level at the input to the hydropower system, which is always far from where the control system is.

Hati

You can install a distributed I/O station closer to the measuring points. Though the connection needs to made with Fiber optics, because of the lenght.

 Thanks, wasn't aware that the S7-1200 works with distributed I/O, are there Siemens distributed I/O devises that work with the S7-1200?

arunrf

 

Hati

You can install a distributed I/O station closer to the measuring points. Though the connection needs to made with Fiber optics, because of the lenght.

 Thanks, wasn't aware that the S7-1220 works with distributed I/O, are there Siemens distributed I/O devises that work with the S7-1200?

 ET200SP series would be suitable for this purpose.

arunrf

 

Hati

You can install a distributed I/O station closer to the measuring points. Though the connection needs to made with Fiber optics, because of the lenght.

 Thanks, wasn't aware that the S7-1220 works with distributed I/O, are there Siemens distributed I/O devises that work with the S7-1200?

The other issues there is, would we need a power supply local to the sensors for the distributed I/O? Thats a lot of extra cable to lay if so.....