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Migration of C7-621 with 313C

Created by: haris_usama at: 1/28/2010 10:31 AM (1 Replies)

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1/28/2010 10:31 AM	Rate (0)
haris_usama Posts: 81 Rating: (2)	Dear Sir/Madam, Please note that I had recently tried to migrate a C7-621 to an S7-313C CPU & OP77A. The old system (C7-621) had three analog inputs connected as current source. I rewired them for the S7-313C CPU and wired them to the integrated analog input of the CPU. I changed the addresses as per the new ones and also set the selection to 4-20ma for channels 1,2 & 3 on the hardware selection. However, I do not get the desired results from the analog inputs. After reading the manual for C7-621 I learnt that it takes current type analog input as -20/+20ma range. When i set -20/+20ma range the 313C CPU goes into stop mode. However, when I use 4-20ma signal it gives output but the result is not as desired. I have two pressure sensors and one pt100 (Connected to a 4-20ma transmitter). Information for Pressure sensor 1: measuring range: 0 - 25bar output: 4-20ma Voltafe:24VDC Information for Pressure sensor 2: measuring range: (-1) - 9bar output: 4-20ma Voltafe:24VDC and one PT100 connected through a transmitter. I was unable to attach the .rar file of the original C7-621 program. Kindly take a look at the scaling of the analog inputs and let me know how to calculate the scaling functions for the migration. Also, how to scale the PT100 with a transmitter in 4-20ma range since I have only used PT100 in RTD connection. Best regards, Haris Usama I IA/DT Siemens Pakistan Engg. Co Ltd
haris_usama Posts: 81 Rating: (2)
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1/29/2010 7:30 PM	Rate (0)
H-H Platinum Member Joined: 7/2/2008 Last visit: 8/26/2024 Posts: 928 Rating: (308)	Hello haris3853 , You have 2 options, 1- Save your effortby usingthe same user program of C7and solving the problem of +/- 20mA. To solve this problem, you should know why the CPU goes to STOP when you download +/-20mA configuration by reading diagnostic buffer. 2- Make a new hardware configuration with 4-20mA configured channels and modify the C7 Program. In this case, youcan use thescalingfunction FC105to scale integer raw data (0-27648 ) to actual measurement (e.g. 0-25 bar). You can find it when you open your program editor under Libraries>Standard Library>TI-S7 converting blocks. haris3853 Also, how to scale the PT100 with a transmitter in 4-20ma range since I have only used PT100 in RTD connection. When you read about FC105 you will find that you set 2 values (High and Low limits)to scale in between. For example, your 1st pressure transmitter has a low scaling value of 0 and high scaling value of 25. In case of PT-100 with pressure transmitter, you have to know the low and high of scaling values from transmitter datasheet. Maybe you can find it like this, 4 mA =-20 C 20mA = 120 C Thenthe low scaling value is -20 and the high scaling value is 120. Best regards. H-H

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