sparkotronic

Hi, I'm looking for some advice or opinions on a control loop that I have been asked to look at and possibly modify. The present system has been there for 10+ years and as far as I am aware it's never successfully worked. My employer has the current set up which is shown in the attached drawing. Using raw water, an acid is added which is then circulated round a contact loop, after the loop, an Alkali is added. The expected end result of the loop is to achieve a specific alkali Ph. The loop has 2 Ph probes which are selectable via SACDA and 2 dosing pumps. The acid dosing pump is controlled by a PID loop where the SP is entered in the SCADA and the PV is measured from the selected Ph probe. The Alkali dosing pump is purely proportional to flow. In the PID block, the derivative is switched off. One probe is just after the acid dose and the 2nd is just after the Alkali dose. My employer wants to be able to control the acid dose by monitoring the Ph probe which is just after the Alkali dose and is also over 10 minutes process time after the acid dose.  I've been told that the system was designed to work this way, even though they have had no successes in running it this way. My wee head can't process how I can control an acid dose while monitoring the after an Alkali has been added, the Alkali will raise the value by 5. There is also only one set of PID parameters. Looking at it, firstly I'd assume that each probe would require its own PID parameters. I have had a play with it, but can't seem to get the loop to react to change and then recover in an acceptable time scale. Could someone give me an opinion on whether the system could operate from the Alkali probe with some PID tweaking? Thanks in advance, Colin

If anyone is interested, I just swapped the dongle and fitted the card and it worked like a dream.

Hi,I'm having issues with my S7 rack communicating via modbus to another device which is the master.I'm a total noob at this and I would like to change out the modbus card in the rack(6ES7 341-1CH01-0AE0).My question is, do I just simply swap the module, looking in the hardware manager of my project, I can see that the card has specific parameters,A re these stored on the PLC and will just simply be written when the rack powers up or do I need to program it?If I need to program it, how would I go about it? Also, is there any specific tool in Simatic Manager that I could use to check that the modbus card hardware is operating correctly and the comms are stable?Thanks in advance, Colin

Hi, I'm working on an installation where the manager asked me to have a look at a comms problem on his Ethernet network. He has 24 MOXA EDS-408AMM-ST switches configured in a turbo ring. Image1 When I ran the ring diagnosis software it showed the ring, but only 15 switches were visible. This was done while connected to the master switch. Image 2 The master switch was also showing the fault light. When I tried to pinging all the switches on the ring, the only ones I could see where the 15 switches shown on Image 1. I then connected to on of the missing switches and tried to ping all switches. I could only see the 9 missing switches while connected to this switch. The 9 missing switches sat in the middle of the Blocked and learning ports of the switches shown . I then looked at the switch 192.168.31.146 this switch showed both P7 and P8 in forwarding mode. This couldn't explain why 192.168.31.146 switch was in learning mode as the manual says that a learning port usually opposes a blocked port. To rectify the error, I had to remove all the copper (RJ45) plugs form the switch with both ports showing Forwarding and then cycle the power to it. Once the switch had rebooted, the ring returned to normal and the fault light went off on the master switch. Do you have any idea how this could be caused? My client is worried about a re-occurrence and I can't find any errors with any of the switches. Up to this point, the system had been running for about 6 months with no issues Also, has anyone had any issues with the Ring Diagnosis software? It no longer works, when I try to run it I collecting information goes to 10% and then I get an error window which says "Now Support Turbo Ring V1 Only!!" I have tried 4 different laptops on the network and each has the same result. The electrician on the installation tells me that he has never been able to conect the ring diagnosis software. I'm using version 2.2 on a Windows 7 64 bit laptop. Thanks in advance for your help,

Hi all, I'm now finding myself being thrust into the world of Siemens Step 7 after 3 years on a Bradley exclusive site. I'm looking for some software to mimic Bradleys trend function on Step 7. I was using a 3rd party OPC trender for the Bradley PLC's and I'd like to continue using this. So....my question is, Can I access S7 PLC's via OPC? If so, what do I need software why and free if possible :) Cheers, Colin

Hi all, Does anyone know of a utility like the Tag Data Monitor Tool which will allow me to put descriptions next to the tags? We are in the process of migrating from PLC5 to CLGX and I want to be able to reference to the existing PLC5 Custom Data Tables. Cheers, Colin

Just to let anyone who is interested in this topic know. I received a conversion kit for a PV1400 today. It was a dawdle to fit and the screen looks 10 times better than any CRT. Well worth the 500 euros.

Thanks for clearing that up for me, it makes much more sense now Cheers, Colin

Hi, Say for instance if the conveyor is running at 62% the bias has a constant of 4.8. Does this increase in output stop when the loop catches up?

Hi, I've been looking at a part of one of the processes in my work place and have came across something I have never seen before. Here is a simplified drawing of the process The PID loop controls the burner output to maintain the temperature at T1. Material is fed into the system at a fixed speed by the feed belt. The material is then sucked through the drying chamber and deposited in a silo by induced draught. On the PID loop there is a variable called the Bias. This is changed by a calculation (%feedbelt speed - 50 X 0.4) So if the operator sets the speed of the belt to anything other than 50%, the bias value changes. The belt normally runs at 60(ish)%. This is a fixed speed set by the operator and isn't normally adjusted unless on a product change. My questions are what is the Bias and what effect does varying the Bias have on the loops performance. I have a very limited experience on PID loops, I did phone Rockwell but they couldn't keep it sparky simple :) Thanks in advance

Thanks for the reply. The oscillation has been coming and going for a few months now, it was mostly going but is now mostly coming! The machine in question has 6 servo's on it, this particular servo is peculiar as the encoder isn't fitted to the motor but runs on a rack and pinion attached to the pusher. I may look at new cable and encoder to rule it out. I did notice that the encoder cable isn't screened, so it could be picking up some noise. Motion stuff is another language to me, I just get by on ladder! What is a feedback noise error? Is it irregular pulses from the encoder? Is there any way in control logix that I can look for this? Thanks again. I think Mr Bradley has washed his hands on me as it is Siemens drives in the application. There was a sharp intake of breath when I mentioned this :) Colin

Hi, I'm looking for a bit of guidance on a problem that I have on one of the machines in my workplace. I have a servo motor attached to a pusher arm which oscillates backwards and forwards when it's not in use. We are using a Logix 5000 CPU with 1756-M02AE Motion control cards. The Servo drive is a Siemens Simodrive 611 I don't have a great deal of experience with motion control but when I look atthe program when the drive is oscillating there are no MAM functions in use. I did speak to an AB engineer regarding the problem, he told me to adjust theGain setting in the Axis Properties in the motion groups. Is this tied into some sort of PID control for the drive? It was set for 20.0 1/s I took it down to 17.0 1/s. This helped a bit but I now occasionally get a feedback noise error. Any ideas on what this error is? Any help would be most appreciated Colin

Thanks for your replies. Is there any chance you could post some code examples on how to cascade the MSG's? I have tried a few things with no success and the PLC in question is a site show stopper when it (or I make it) fails! On the duplex, am I right in saying that 1/2 duplex means that the side card can only read or write and full means it can do both at the same time? I changed the side card a few months ago to the RJ45 style but I didn't know about the settings. Would making this simple change make a big difference? The PLC also has other PLC's reading from and writing to it, the whole thing looks messy to my untrained eyes. Thanks in advance

Hi, I'm still fighting my way through PLC5 and Ethernet coms. I'm having problems with one of the PLC's on my work network. It occasionally drops off RSlinx and we lose all coms to the processor, when this happens I can access the ENET side card through IE so I don't think it is a network problem. The PLC in question has about 40 MSG blocks which constantly trigger. I've read that this can cause issues with time outs ect. The ENET side care is also set to 10mps 1/2 duplex, I'm hoping to change this on our next maintenance day to auto neg as I've installed new 100mps cisco switches. I'm also hoping to add diagnostic files to the ENET cards as well to try and get more data. The logic below is a sample of how it is done. I've read that this is not a good practice as you should cascade them. I have tried this in a few different methods with little success. Could anyone shed some light on this issue? I have 15 PLC's on the network and all MSG's are triggered the same way. I've got a Rockwell Ethernet course booked for next year and an arms length of questions to ask ;-p Thanks in advance, Colin

We are in the process of doing this, but as a short term solution I thought it might get us out of a bind.