S7-1200 analog input board problem

Which board and how many other analog inputs does the board have?

Did the manual for the analog input board you have suggest grounding out all unused analog inputs?

Is your input module configured for voltage or current?

What Hz?  400?

You say 1 cycle update (minimal averaging).

If you want to read it more often than the PLC scan time, you can run a periodic OB that runs every 0.5 msec and get the current value.

Hopefully something in all that helps you find the issue. 

Tecla

I try to use the board to read input as fast as possible, but

I must drive the board whirh a low impedance source, since with the imput open i find about 1.7 volt

at the imput terminal and a board reading according to this input level.

If I connect a a voltage ramp 0-2Volt rising from zero to maximun lelel in 40 msec I read a maximum

level of 19000 reading instead of the 22100 expected.

With a rise time equal to 4.5 msec. and sampling time 0,156 msec. this seems to be not correct.

I was expected to can read a fairly correct value whith the 0-2Volt ramp in 5 msec.

The board is configured whith 1 cycle levelling.

What is my error or may be i have in hand a defective board ?

S7-1500 family has a fairly fast analog input module, but the s7-1200 does not.

For the task you are attempting, if the load cell is slow, you can do it by sampling every 1msec by using a periodic OB that runs every 1 msec and directly access the analog input value using IWxxx:P and sample / compare / save if new peak found during cycle.

In the area I work, we use PC with National Instrument PCI DAQ boards for very high speed analog value sample logging.  We use their "low end" boards for multiplexed 16 channel 250kHz.  They have faster, and if you need all 250kHz, you just sample one channel.

Hope this helps since IBN is spot on in their post about this being an inappropriate expectation for the s7-1200 PLC analog input. 

Tecla

I have an S7-1211 with an analog board on it.

I have configured the filter to 400Hz 1 cycle and i take the reading when an interrupt is generated by an HSC.

Before I have not seen the setting of filter frequency, so now with the correct setting the results are better.

At half the required cycle frequency the result is fairly ok.

Does exist some way to set the filter frequency to 1 KHz ?

We are planning to use many PLCs configured in this way to measure the peak value from a load cell. The signals are as in the scope wiew attached.

Pin O- is connected to M terminal of the PLC, ground terminal of the PLC il left open.

The system is on a test bench.