Remote sensors : clamping diodes and input filtering?

In a data-logger I am designing right now the sensors will be placed some 3 meters away from the central unit. I'll have an RTD PT1000, a capacitive humidity sensor, a digital pressure sensor and two strain gauges.

I have two questions on this configuration, regarding two topics that I'm not very familiar in :

1) Do I need any clamping diodes at the connection point of the sensors to the PCB?
2) Any filtering before the amplification stage? I'm mostly concerned on EMI (both inductive and conductive). Are filters really necessary? For example the NFM21C or the BLM series of Murata.

Nick

hi Nick,
Whats the environment the sensors are working in.? ie: close to other 'noisy' equipment , outdoors, etc.?

Hi,
I would say close to other 'noisy' equipment. But it is important, too, except for the inductive EMI that the device does not produce any high levels of EMI.

nickagian said:

Hi,
I would say close to other 'noisy' equipment. But it is important, too, except for the inductive EMI that the device does not produce any high levels of EMI.

Click to expand...

hi,
If the sensors are controlling a critical process I would always fit high quality filtering and clamps on the sensor inputs at the pcb.

If any RS232 equipment is part of the pcb, you can get filtered 'Dee' type connectors.

In case you dont have a sensor app pdf, see attachment

ericgibbs said:

In case you dont have a sensor app pdf, see attachment

Click to expand...

hi,

thanks for your help. I had indeed downloaded and studied the attached pdf. However, I am a little bit confused with all these different options and choices.. I would use a combination of one BLM18 in-series and one NFM21 to ground. Does that sound logical? Is there any difference between the analogue and the digital signals (because I have also a digital remote sensor)?

And regarding the clamping diodes, because I'm not very familiar, what kind of protection will they provide in this case of the sensors? The diodes will protect against spikes from outside that would create high voltage in the running cable and thus perpaps burn the analogue interfaces?