Sorry if this is basic. Internship, the old line at the plant, my first analog signal. Water tank, 4 metres tall, level transmitter 4 to 20mA into an SM 331 on a CPU 315-2 DP, STEP 7 5.6. The channel is PIW 256.

I took PIW 256 into a DINT with ITD, divided by 6912 because 27648 over 4 metres is 6912 counts per metre, then multiplied by 25 to get percent. The HMI shows 0, 25, 50, 75 or 100 and nothing between. I watched it fill, it stayed on 25 for ten minutes then jumped to 50. Below about a metre it shows 0.

Tried: swapped the transmitter for the spare, same. Checked the channel is set to 4 to 20mA in HW Config, it is. Checked the two wires at the terminals.

I used DINT because I read that REAL is slower on the 300. Is the card resolution too low? Someone said it is a 12 bit card.