kilolima

Thank you all for the advice. It is invaluable. I was going to convert the integer ADC level to floating point voltage (in this case, between 0-5V) to make the sum smaller. Your suggestion of using registers seems to be more elegant. Do you mean, for the example of 42356, you would put 42 in one memory location and 356 in another and later on, put them back together by 42x1000+356? Would you please explain in more details? Thanks again to everyone for the help. Much appreciated!

I am trying to implement the peak detection and integration of an input signal with MircoLogix 1500 and RSLogix 500. The input is from the analog input module (1769-IF4I) stored as an integer. I am using a clock signal which I build out of a couple of timers trickering each other to downsample my input signal and load it into a sequencer with the SQL instruction for the time delay implementation. For integration, I am using an ADD block that essentially performs N7:0 = N7:0 + N7:1 on every clock on duration (i.e. T4:0/EN). This causes fault and halts the processor due to the explosion in the sum. To investigate the problem, I created a simple program to test this effect with the following rung: XIC B3:0/0 ADD N7:0 N7:1 N7:0 (N7:0 assigned to 0 and N7:1 assigned to 1 innitially). As soon as I toggle B3:0/0, N7:0 grows continuously until I toggle B3:0/0 off. There seems to be some unstability when adding to itself. So, I decided to try with the following two rungs: XIC B3:0/0 ADD N7:0 N7:1 N7:2 MOV N7:2 N7:0 (N7:0 assigned to 0 and N7:1 assigned to 1 innitially). which should perform N7:2 = N7:0 + N7:1 N7:0 = N7:2. As expected, I got the same result. The summation grows over the roof. With this said, my peak detection also failed because it involves summing as well. I would appreciate any clues and pointers to this problem. I am quite a newbie to PLC and didn't have any formal trainning in it. Maybe there are conventional ways of simple operations, such as x = x + y, that I am not aware of. I would appreciate any recommandations on further readings/recipes, other than the downloadable PLC book by Hugh Jack, which I have already got. Thank you very much for your help.

Thank you very much for your detailed explanation. Now, I see the difference of OTE and OTL. I got it to work with OTL and OTU instead of simple OTE and CLR just as you suggested. (I changed to OTU as well because CLR has no effect when the bit was set with OTL. It has to be unlatched by OTU.) Here is a screen shot of the working ladder logic: Thank you so much again. That was extremely helpful. Greatly appreciated it!!

I am new to PLC, and I am using MicroLogix 1500 with RSLogix 500. I want to log the analog input every fixed time interval (e.g. 0.1sec). The DLG block does a data log every time when the rung goes from false-to-true. So, I am trying to build a clock signal to toggle that rung using TON timer but without success. My attempt is as follows: 1) B3:0/0 is used to turn on/off the TON timer rung and the DLG rung. 2) When the timer reaches the preset time (i.e. T4:0/EN becomes true), I reset the B3:0/0 so that timer and DLG rungs will be turned off. 3) I have another rung that has XIO on T4:0/EN so that when the timer is not enabled, I would set B3:0/0 to turn on the timer. The last step 3) is supposed to be my looping mechanism to keep the toggling going. But I think I am missing something. It is toggling freely and continuous, not at the set time interval. Is my approach wrong? Is there another way or more conventional way to do data logging? My ultimate goal is to log an analog input signal (via the analog input module) every 0.1sec for a duration of 90sec and preform an integration of this signal. This signal is proportional to a gas flow. The integration with time will give me the total gas volume which is what I am trying to determine. I will appreciate any suggestion or pointer. Thanks a lot! Edit: Here is a screen shot!

Thank you very much for the recommendations. Really appreciated. I will phone up some local distributors and see what they can do for me. Thanks again. And Happy Holiday.

Thanks for your reply, TW Controls. Currently, we don't have any PLCs in the whole facility and no one in the facility has any knowledge or experience in PLC. So, I am particularly interested in picking something easy to start/use and flexible in terms of compatibility and expandability. So far, I found Automation Direct (DirectLogic) has the lowest cost PLCs. Is there any disadvantage of using that brand of controllers? I am located in Toronto, Canada. I took your advice and checked Automation Direct's support page. They do have an affiliate in Toronto.

I am new to PLC, and I have a project that requires some temperature sensing/feedback and valve controls. It is a part of a bigger automation system, and it will expand further to integrate with other parts of the system in the future. The bigger system has optical isolated RS-232, GPIB and CANBus in place for device communications. Most equipment in the facility has been around for more than 20 years. This new addition will likely to be there for a long long time. So, I am concerned with compatibility and how easy to buy replacement or additional parts in the future. I saw many different companies that make PLC products, Rockwell (Allen Bradley), Omron, Automation Direct, etc. The price difference is quite significant between, for example, Rockwell and Automation Direct. Are they all compatible with each other, in terms of both hardware and software? Is one better than the other for a given application? In general, I would like to get some pointers about how to choose the right controller. I appreciate any of your help. Thanks in advance.