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Modubus RTUs Technical Support Needed !!!

Created by: jfann at: 6/10/2008 4:07 PM (8 Replies)

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6/10/2008 4:07 PM	Rate (0)
jfann Posts: 7 Rating: (0)	Hi all, I've installed 4 of the milltronic BW500 integrators on our site formonitoring the aggregate productivity. The data we've collected onall 4integrators were accurate (reading off the LCD screen on site), but once the datawere transmited through the on site Modbus RTU Protocol,2 out of 4 data were reporting the exact data shown on the integrator LCD screen, but the other1 data we've received at the office were complete off (EX. site reading was 46 Ton/Hour, we were getting 897846)...The other won't even communicate..its says RTU back off/ No RTU. Please advise. Note: All 4 integrator were daisy chain to feed into1 communication output. Regards,
jfann Posts: 7 Rating: (0)
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6/10/2008 4:32 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 12/26/2024 Posts: 12313 Rating: (2695)	Hello jfann? Is the value you are getting a wrong reading on a 32-bit value, perchance (DINT or REAL)? Check it out in the data mapping provided for your unit. If you are requesting 4 INTs and one of them i using 2 ints, you might be having only 3 values read by your master. Since the first 2 values are read correctly, I would preume that they are 16-bit values, and interpreted as INT registers, so that should be reflected in your unit's Modbus mapping. Let us know what you find. Hope this helps, Daniel Chartier

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6/10/2008 5:46 PM	Rate (0)
jfann Posts: 7 Rating: (0)	Hi dchartier, Thank you for your advice, I'll check the issues you have listed and I'll get back to you asap. Regards, Jason Fann
jfann Posts: 7 Rating: (0)
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6/12/2008 5:33 PM	Rate (0)
jfann Posts: 7 Rating: (0)	Hello Daniel, Is the value you are getting a wrong reading on a 32-bit value, perchance (DINT or REAL)? How would I know if the value I am getting is on a 32-bit value?from which device and how? Please define DINT or REAL. Check it out in the data mapping provided for your unit. Data mapping from which unit? The BW500? If you are requesting 4 INTs and one of them is using 2 ints( Please define "one of them", which component?), you might be having only 3 values read by your master. Since the first 2 values are read correctly, I would preume that they are 16-bit values, and interpreted as INT registers, so that should be reflected in your unit's Modbus mapping.
jfann Posts: 7 Rating: (0)
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6/12/2008 7:08 PM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 12/26/2024 Posts: 12313 Rating: (2695)	Hello Jason; Looks like we'll have to go through basics a bit, if you don't mind. Modbus is a relatively old protocol, adapted to the Modicon processors of it's day (late 1980s). it only works with 16-bit registers, signed INT values (-32768 to +32767). Whatever address you request from the slave (the Milltronics unit, in this case)., it represents one 16-bit register. So if you are rrequesting address 40,090, named Parameter, you will see in the Modbus mapping of the BW500 that its allowed values are 0-999; so they fit inside the 16-bit INT limits. Accordingly, the next register shown on hte Modbus mapping is 40,091, called Primary Index, and its values range from 0-6---a INT value. Now, let's look a little lower, at register 41,010, Rate; you might notice that the next available address is 41,012, Load; so 2 register addresses are reserved for Rate. And in the description it clearly says that it is a 32 bit value. By the way, you do have the BW500 instruction manual? I found it on the web, at this address: www.lesman.com/unleashd/catalog/belt/spl_0625.pdf Open it at pages 124 and next for details of the Modbus mappings and data formats. Why do we need to use 32-bit registers? Data that you want to exchange could easily have values of more than 33,000, no? Totalized gallons, KiloWaltts, frequencies or other parameters are often in large ranges. In that case we use DINT (Double-Integer) values, same as INTs but covering 2 16-bit registers (with values accordingly much larger, from-2147483648 to +2147483647). Or you might wnat to send 32.3, or 100.009 (a floating-point value, a REAL variable). I won't go into much details about this format, but trust me, it needs 32 bits. So this is what I was talking about in my first post. When you do a Modbus request in the master, you use the slave's amodbus address, the function code (3, Read registers,in this case, to access the 4x,xxx registers of the BW500) and a number of registers (remember, 16-bit registers only). So if you have 32-bit values sowhere that you ewwant to read from the master, you need to count 2 registers for this value. There's more to Modbus than this of course,, but let's start by examnining my original questions in the light of these explanations. We'll see if we need to go further depending on your answers. By the way, could you tell us what values you are tryiing to transfer from each BW500, and which ones are giving you problems? Also, a copy of your Modbus request for one slave could be helpful. Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 6/12/2008 7:10 PM
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6/12/2008 8:28 PM	Rate (0)
jfann Posts: 7 Rating: (0)	Hi Daniel, The value I am trying to obtainare the tonnage rate and totalizer 1 and totalizer 2 from the integrators. We have 4 ints on site, 2 of them are giving the correct value,one of them is giving me some HUGE numbers, and one of them won't even response. The attachment below basically shows the infomationI am getting in the office. Thank you very much for your input into this matter.Last question:I was wondering "How would I be able to access to the Moudus Register Map?" All I have is the Dophin plus software. Regards, Jason Fann Attachment data.zip (403 Downloads)
jfann Posts: 7 Rating: (0)
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6/13/2008 5:39 AM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 12/26/2024 Posts: 12313 Rating: (2695)	jfann Hi Daniel, The value I am trying to obtainare the tonnage rate and totalizer 1 and totalizer 2 from the integrators. We have 4 ints on site, 2 of them are giving the correct value,one of them is giving me some HUGE numbers, and one of them won't even response. The attachment below basically shows the infomationI am getting in the office. Thank you very much for your input into this matter.Last question:I was wondering "How would I be able to access to the Moudus Register Map?" All I have is the Dophin plus software. Regards, Jason Fann Hello Jason; You mention Dophin software, which I found out is a configuration/monitoring software for the Milltronics unit. In this case, this will not help you. You need to see what is happening in the Modbus master. In short, a Modbus master requests some data from the Modbus slaves it is connected to. Someone, generally the master's programmer, will read the manual I asked you to look at, determine what available values he/she wants to bring into the master, and inside the master's program setup a Modbus "job"; this job is described in the BW500 manual in the first pages of the Modbus description, around page 121. By the way, what is known as the Modbus slave register mapping is the document I asked you to examine yesterday, in the BW500 instruction manual, pages 124-125.... The master's job request has no idea what data you want to collect; it only sets the start address (in the slave's Modbus mapping) and the number of 16-bit registers you want to import from the slave. It is the responsability of the master's programmer to make sure that he requests the correct addresses and number of registers from the slave to be able to read the correct values from the slave. Any further manipulation of the data (and we will need to examine this once we have cleared this first important issue) is also the programmer's responsability. Now you mention Rate and 2 totalizers (originally you mentionned 4 values, what is the fourth?) as the data you want to collest; these 3 registers use (3 data * 2 16-bit register per data) = 6 16-bit registers (that might be a total of 8, if you are requesting 4 32-bit DINT values). If your master's job is requesting only 4 (because the programmer presumed he was looking at 4 INT values instead of DINT values)then you are mis-reading the data, and that would give you something like the results you are getting. So, at this point, we need to know if that is the source of your problem. Someone has to examine how the master's Modbus jobs have been configured. If you have no idea how this was done and you have no knowledge of the Modbus master"s programming software, then I strongly suggest that yout talk to someone who has that expertise, especially if you need a quick resolution of the problem. If you have the time and the expertise, then open the master's Modbusjob configuration/program and tell us how many registers are actually requested from each slave and at what address. Hope this helps, Daniel Chartier
	Last edited by: dchartier at: 6/13/2008 5:44 AM Last edited by: dchartier at: 6/13/2008 5:41 AM
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6/13/2008 6:10 PM	Rate (0)
jfann Posts: 7 Rating: (0)	Hi Daniel, Thanks again for your quick response. To clairfy the confusions from the e-mail I previously sent you, I meant 4 integrators connected through daisy chain (@ One site} and each integrator was ask to send 3 datas ( Rate, Totalizer 1 and Totalizer 2). Jason Fann
jfann Posts: 7 Rating: (0)
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6/15/2008 8:15 AM	Rate (0)
dchartier Grandmaster-Expert Joined: 9/27/2006 Last visit: 12/26/2024 Posts: 12313 Rating: (2695)	Hello Jason; I recommend you talk to the programmer of the Modbus master PLC at this point. He should be able to check whether the master's Modbus jobs covers the correct amount od registers from each slave. He can also verify wat manipulations are required on the data that he recieves from the slaves (byte or word swapping could also be an issue in your problem). By the way, you never mentionned the brand and model of the Modbus master you are connecting your BW500 units to. Although it doesn't make much difference (Modbus is platform independant, if it is designed properly) that info could help us help you. Hope this helps, Daniel Chartier

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