Analog input is unstable

Hi Ryan01,

I addition, please check shielding and earthing for field cabling.

I used a Fluke DMM and gave a direct 8.000 mA to one channel, even in this case PIW value had variation.

I think the module is faulty.

Hello!

To begin with, I want to say sorry for my English... On the forum, I often come across questions about unstable values at the inputs of high-speed analog input modules (AI /HS). Instability is observed even when a signal from the calibrator is applied to the input. On conventional analog input modules (non-HS), the signal is stable. The problem is that for high-speed modules, it is NECESSARY to install a bracket of the shielding element (for S7-1500 it is A5E42031409-AC). Further, according to the connection diagram of the module. As soon as you connect the shielding element and the negative wire (I-) from the analog sensor (or calibrator), you will receive a stable signal at the analog input. On conventional (none-HS) modules, the signal is stable even without this connection and this is misleading. I repeat - for HS type modules, this is a mandatory connection for a stable signal at the input. I will be glad if it helps someone.

Mr.V

Maybe AI signals get noise from frequency drivers or something like that? did you use shielded cable and split from power cables?

 I have experimented with modules of various types in laboratory conditions, without interference, with stable power supply and shielded wires. Installing the bracket of the shielding element on the front connector gives an amazing result for the HS module. There is no such effect on a conventional module - it already gives a stable result of converting the input signal.

0_Einstein

Conventional (not high speed or high function) modules have slow update rates, and have automatic filtering with the way the circuits are designed with a slower update rate, so they smooth input data automatically between updates.

 This does not mean at all that a faster module, with a similar connection and settings, should produce a different result, in my opinion. However, it is. The requirements for connecting HS modules are more stringent.

The essence of the problem with an unstable signal to HS modules has been solved - the connection scheme plays an important role.