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CP341 MODBUS master with EM6400 in PCS7

Created by: Mist9 at: 4/29/2013 11:50 AM (13 Replies)

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4/29/2013 11:50 AM	Rate (0)
Mist9 Advanced Member Joined: 3/19/2012 Last visit: 6/6/2024 Posts: 18 Rating: (1)	Conzerv energy meter EM6400 series are communicating but the result is sluggish. There are 18 numbers of meters connected as shown in the attached file 'EM6400 wiring'. Customer used profibus cable to take all the meters in loop. CP341 is used as modbus master. Software used is PCS7 v8.0 update 1, CPU 416-5-H PN/DP. Necessary driver and license were installed. The baud rate is 9600, parity even and stop bit 1. Unique slave addresses are assigned to the respective meters. S7HMODM3 block, EXSQ_MOD bock and MODMR_R blocks are used for reading holding registers from the meter. The problem I am facing is the slow communication and very intermittent when communicating with all the slaves. Various problems are been faced which I have mentioned in a word file as found in the zip folder. Attachment Modbus Issue.zip (422 Downloads)

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4/29/2013 1:27 PM	Rate (0)
manmeet Gold Member Joined: 1/3/2006 Last visit: 2/19/2024 Posts: 726 Rating: (71)	HI I have not used the library which you are using but refer to manual of the library to check if it is OK that MODMR_R are in OB33 whereas S7HMODM and EXSQ_MOD are in OB34. Also check the sequence of all the called block as per manual. Also check the CALLING TIME of OB33 and OB34. Also first check communication with only one meter and check if its healthy. Read as many register as you want to read from this block. If everything is OK then only proceed to hook another meter with same settings and check if everything is OK. Just revesit your hardware settings it shall match with that of in EM6400. Regards Manmeet

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This contribution was helpful to 1 thankful Users Mist9

4/30/2013 8:47 AM	Rate (0)
Mist9 Advanced Member Joined: 3/19/2012 Last visit: 6/6/2024 Posts: 18 Rating: (1)	Hi Manmeet, In the maual(as attached) for the library says that S7HMODM3 and MODR_R can be used in a different OB's. The meters were wired as per the EM6400 manual. Firstly I had connected only one meter and kept the meter in the simulation mode and I was reading upto 20Registers in one query.Later when I switched the meter in RUN mode I was not able to read more then 6 registers also the response was slower. While reading multipe slaves and requesting different slaves in next query the reponce was very sluggish.Thedrivers loaded in CP341are proper and they match with the set parameters in the Meter. Attachment PCS7_S7HMODM3_v3.0_E.pdf (469 Downloads)

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4/30/2013 11:45 AM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	My experience has taught me that is very difficult to fault find on muilti-drop networks with a large number of slave devices. You could have your work cut out for you here. From your comments, it would suggest that the meters are not very well designed. They really shouldn't suffer from communications delay when running. This would suggest that they do not have enough CPU power to service the communications port as well as performing its normal duties. You could try to vary the ammount of data (registers) you request per telegram to see what effect that has on the update speeds. To keep things simple you should do this with a single meter in isolation to eliminate any influence from the other meters on the network. Start by just asking for 1 register, then keep increasing this up to the full amount that you require. Note the update time for each test. The baud rate, parity etc. errors you are seeingare known as framing errors and are not normal. These are caused by the CP card losing synchronisation with the data stream. This could be caused by a faulty slave device, faulty wiring on one or more slave devices or poor termination on the network bus. Try building the network up one slave at a time until the problem starts to become evident. This might allow you to track down a possible faulty slave device / wiring. Do you have termination resistors fitted on the last slave device? It is normal to fit a 120 Ohm terminating resistor between the RX/TX+ and RX/TX- wires on the slave device that is furthest phusically from the master device.
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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This contribution was helpful to 1 thankful Users Mist9

4/30/2013 12:33 PM	Rate (0)
manmeet Gold Member Joined: 1/3/2006 Last visit: 2/19/2024 Posts: 726 Rating: (71)	Hi Firstly I had connected only one meter and kept the meter in the simulation mode and I was reading upto 20Registers in one query What you mean by meter in simulation mode? Also as Smiffy mentioned is everything healthy with one meter (in isolation) in Run mode?

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4/30/2013 1:29 PM	Rate (0)
Mist9 Advanced Member Joined: 3/19/2012 Last visit: 6/6/2024 Posts: 18 Rating: (1)	hi, The manual of the meter says that the meter has built-in impedance matching design.The meters are however closed loop wiring as seen the image file zipped in my first mail.The driver setting for CP341 is half duplex and the device are terminated at pin no. 4(-) & 11(+). I had first requested minimum amount of registers i.e. 2 and then increased further.Maximum values recieved was 3(float value) with the request of 6 registers which took long time. There is a setting in the meter to make it operate in simulation mode and run.In simulation mode meter would generate value irrespect to the load connected to it and in the Run mode it would give the actual values according to the load. With only one meter in Run mode I am able to fetch only 4 registers and that takes about 5 sec to update. Thanking You

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4/30/2013 4:01 PM	Rate (0)
smiffy Platinum Expert Joined: 1/17/2007 Last visit: 10/21/2024 Posts: 1547 Rating: (537)	If it is taking 5 seconds just to read 4 registers from one meter, then I cannot see how you can ever make a success of this. The meter is obviously just not up to job. Something else I just noticed from your wiring diagram. You have a ring topology (the wires are looped back to the CP card at the end of the bus). This topology is possible, but not recommended for RS485. The bus topology is the best topology for RS485. The manual suggests testing the unit with modscan. Have you tried this to see have quickly it responds to modscan? This will confirm that the problem is the meter and not something else.
	Programming today is the race between software engineers building bigger and better idiot proof programs, and the universe producing bigger and better idiots. So far, the universe is winning...
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8/21/2013 10:10 PM	Rate (0)
Chandra Tiwari Posts: 247 Rating: (2)	Hi Pinkesh, I have PQM meter on modbus. I have 23 slaves on single modbus loop with FB7 and FB8. It is working fine when no. of slave is 1 or 2, but if i use no. of slave 10 then the FB 7 showing error on every and done bit after 10 sec. and this time Done bit is coming after 10 sec, error is coming every second and NDR is also showing after 10 sec. please help. Regards, RaviS
Chandra Tiwari Posts: 247 Rating: (2)
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8/22/2013 8:18 AM	Rate (0)
Mist9 Advanced Member Joined: 3/19/2012 Last visit: 6/6/2024 Posts: 18 Rating: (1)	hi ravi, For my projectI had not used FB7 and FB8. Try changing the OB scan time. As per to my knowledge each scan cycle would readone meter at a time.If you use 10 meters the scan cycle would also increase and time to update values for each meter will also be affected. Regards ,

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8/22/2013 4:48 PM	Rate (0)
Chandra Tiwari Posts: 247 Rating: (2)	Hi Pinkesh, Thanks for reply. Please let me know from where to increase this time, i am working first time on SIEMENS PLC so i dont have much idea, please help. Regards, RaviS
Chandra Tiwari Posts: 247 Rating: (2)
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