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JayA

Analog and thermocouple input for micro plc

7 posts in this topic

Ever need a single analog or thermocouple input for a micro PLC such as CPM1A, CPM2A or CPM2C.  Most manufacturers offer these inputs, but you wind up buying some multiple of in and out which leaves you with extra cost and unused I/O. Calex manufactures a line of analog to frequency signal conditioners which drives Omron or other micro PLC high speed inputs.  I have used them and can provide code for reading and scaling these units. Here's the link: http://www.calex.com/cgi-loc....0760362

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Jay Thanks for site info, am looking at the 430 bridge sensor. Have a project where we are use a load cell to measure a force on a test machine. To make long story short, pulls a garment until 9 lbs of pressure is measured, then continues to pull garment until 10 pounds of pressure is met. At the moment, been working with a integrator who is using a Beckhoff Strain Guage input module as the I/O. The results of the load cell as garment is being pulled is stored about ever 3-4ms. Looking at possibly building over 100 more of the units, and looking at using products that would make the machine more user friendly when troubleshooting. At the moment, it is a Advantech Industrial PC, running Twincat Softplc software and Beckhoff IO modules. Application also is using a custom Operator screen that was developed by integrator using C++, and a Sybase Ianywhere Database type product. Works fine, but due to lack of experience with this type of software and some of the communications problems that I have seen with the Beckhoff IO modules with the prototype, have approached the integrator about using the Advantech Industrial PC to handle the Ianywhere Database Engine to continue to communicate with a Network Drive for styles,size,etc. of garments being tested and transfer test results to network, but replace the C++ Operator Screen with a more easily understandable HMI Software such as Indusoft (low runtime cost), and have the Advantech connect to a OMron PLC that will actually be running the testing. Integrator has concern about using a omron plc and a load cell (thermocouple) type input module. Would it be possible to connect a load cell to the 430 bridge sensor, have it convert it to a 4-20ma type output which could then be connected into a analog input on a Omron CJ1. Integrator has concern that if a product such as the 430 bridge sensor would not respond fast enough. The results of the load cell needs to stored approx. every 2-3 seconds. Best I can tell the CJ1 is capable of scanning 320 I/O-10 steps @ 0.1µs Your advice or suggestion would be very helpful.

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The CJ1 AD--- V1 cards can convert at 250us at 0-8000 and 1ms when set to 0-4000 so i think that 2-3 seconds should be fine. In my experience the conversion from a weigh cell to 4-20mA should be well within the specifications of 2-3 seconds .... By the way Jay, i have seen similar units used for tank monitoring at a winery, certainly saved on analogues.... standard inputs were used also...

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My fault, I meant that results should be measured and stored every 2-3 ms. Integrator is concerned that the scan and process time may not be fast enough which is why he is still leaning toward some type of industrial pc and IO modules, but when you multiply the cost time 1-300 additional machines, could be quite a difference in price. Thanks

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Jay Could you provide some sample code? Considering using one of these units to convert a load cell input to a 4-20ma signal to feed into a Omron PLC analog input module to measure a force of a garment as the garment is stretched. Garment will be pulled to it reaches a measured force of 9lbs and then will save and average the loadcell input until the force reaches 10lbs. and also measure the distance until the 10lbs is reached, and then save the results. Thanks

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The operative word in the above quote is frequency. The units I referred to converted analog signals to pulse out. Therefore, micro PLCs that did not have analog capability could use the high speed counter inputs so often available on micro PLCs to convert the frequency to an analog value. What you are proposing is a convertor that just converts one form of analog signal to another more common analog signal. All the magic happens in the convertor. There is no need for additional code.

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Thanks Jay Am considering using a CJ series Omron plc and a Phoenix contact line guage,load cell unit on the project that I have posted about. I apologize for my making myself more clear, was in a hurry to get to a meeting about another project that i have to do, and did not explain with enough detail. but after looking at the unit you posted about, we are also considering on another project, (autoclave) that only has a few inputs and outputs and a pressure transducer (0-10v) connected to one of the units you posted about and one of the small cpm2a plc units. I have a few of the cpm2a 20 I/O brick units that I could use to build on a prototype without having to spend the extra money for a PLC system such as a CJ unit or CQM1H Would be very cost effective if rebuilding multiple machines. At the moment, I have to come up with a budget cost to replace the controls in 17 machines, and the small cpm2a with the 20 I/O points is a very good possible solutions, if the transducer signal could be very efficently converted to a frequency signal and fed into a high speed counter input. Thanks for info.

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