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High Rate of change Alarm!

Created by: Was at: 8/8/2006 6:05 PM (7 Replies)

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8/8/2006 6:05 PM	Rate (0)
Was Posts: 11 Rating: (0)	Hi, I am working on Simatic PCS7 V6.1. Well, I want to know whether there is a block in the Block Library that gives us 'time rate of change' of some Analog quantity. To be precise, I have to give 'High Deviation Alarm' when the rate of change of temperature exceeds '10 Degrees/minute'. If I am recieving temperature from field how can I achieve the desired solution. Regards, Was
Was Posts: 11 Rating: (0)
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8/9/2006 8:19 AM	Rate (0)
Nemo Posts: 3149 Rating: (171)	Hi if you place your CFC with your driver block in a OB/taskgroup which is called/executed every 10 minutes you can reach your goal quite easily. You can set the time ranges for your S7-CPU OBs in HW-Konfig. nemo
Nemo Posts: 3149 Rating: (171)
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8/9/2006 9:35 AM	Rate (0)
PRK Posts: 38 Rating: (2)	Hi I think you want to implement "Gradient Monitoring". You can compare the Present Value with Previous Value every 1 minute for the Change in value you want to monitor and store the present value as a previous value. So every 1minute you will compare for the difference and store the present value to the previous value memory location. This function is inbuilt in Cemat - (Cemat Automation) Measured value block.With this block youcan monitor for both Positive and Negative Gradient. Hope this information is usefulto you. Regards, Krishnan
PRK Posts: 38 Rating: (2)
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8/9/2006 10:22 AM	Rate (0)
Was Posts: 11 Rating: (0)	Thanks for the replies! Nemo, I think there is a major drawback in ur suggestion. Such a huge scan-time cant be used if there is also some other critical alarm associated with this Temperature (e.g., High High or Low Low that causes Emergency shutdown). PRK, you are right. I want to implement 'Gradient Alarm' but not on the basis of two values like at the start and stop of minute. In this way we are going to loose if there came some changes during the span of minute and returned normal. Well, I dont have the License for Cemat (I assume it requires a License). Another thing that our Process is non-Linear. This means that if we r required to alarm at 30 Degress/minute, we cant give alarm at 2 degrees/second. So for me the problem still unsolved. I request all others to share suggestions. Regards Was
Was Posts: 11 Rating: (0)
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8/9/2006 10:36 AM	Rate (0)
Nemo Posts: 3149 Rating: (171)	Hi, you could program a block in SCL for your purposes, where you are reading your analog value and checking e.g. by comparing timestamps from your S7-CPU the e.g. last ten values. You can store this temporary values in a datablock nemo
Nemo Posts: 3149 Rating: (171)
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8/9/2006 1:41 PM	Rate (0)
Was Posts: 11 Rating: (0)	Thanks Nemo! I have written a block in SCL and that is working fine. Regards, Waseem
Was Posts: 11 Rating: (0)
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12/5/2006 7:52 PM	Rate (0)
John Locke Posts: 28 Rating: (0)	I also am looking for a Rate of Change Alarm, I am amazed that this basic functionality is not included within the standard MEAS_MON block! [:cry:] Yet again I have to spend time writing a block to perform standard functions, is it just me oris the standard CFC library sadly lacking in usefull blocks? I'm guessing that longtime experienced CFC users have built up there own library of custom blocks they can use, however for new users the out of the box library is somewhat frustrating. [:mad:] I've no doubt you can buy other librarys from Siemens for a price, how do other people find it? is there a secret website of freeware blocks to play with? [:D]
John Locke Posts: 28 Rating: (0)
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12/7/2006 12:58 PM	Rate (0)
April Posts: 1776 Rating: (95)	Hi, just start here to post Your blocks. Make a short description. And hopefully other will follow. Best regards
April Posts: 1776 Rating: (95)
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