CR4 - Thread: Use of Temperature Transmitters

RDGRNR Guru Join Date: Dec 2009 Location: San Antonio, TX USA Posts: 859 Good Answers: 28	#1 Re: Use of Temperature Transmitters 10/28/2010 8:41 AM
	You have to use a xmtr (4-20mA) when you don't have an RTD input module for your PLC, you can connect the RTD directly to the PLC when you do. Analog input modules are typically better for applications where signal distance and strength are an issue. __________________ "Do not worry about your difficulties in Mathematics. I can assure you mine are still greater". - Albert Einstein
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ele1 Participant Join Date: Oct 2010 Posts: 4	#3 In reply to #1 Re: Use of Temperature Transmitters 10/30/2010 1:25 AM
	hi i agree with you ; but how can we know if PLC has an RTD input module or now
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ranandkumaric Participant Join Date: Oct 2010 Location: INDIA, chennai Posts: 1	#4 Re: Use of Temperature Transmitters 10/30/2010 9:27 AM
	hi, Frist check ur PLC config, if it support the 4-20mA i.e it should support Anolog Input, then u can directly connet your RDT to PLC anolog input, or else u have use the transmiter.
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Phys Guru Join Date: Feb 2006 Location: middle of nowhere, Pennsylvania Posts: 618 Good Answers: 13	#5 Re: Use of Temperature Transmitters 11/04/2010 8:16 AM
	Another case where a transmitter may be required is where there is "noise". (electro-magnetic interference - many solenoids, VFD run motors, etc.) An RTD with prewired cable usually has a cable that is not shielded. The cable run from a transmitter to the PLC cabinet is usually a shielded cable with the shielding grounded at the PLC cabinet. In this situation, the RTD is connected very close to the transmitter, so the majority of the run to the PLC will be shielded. I have never seen interference affect an RTD, and I have run as many process skid applications with RTD's cabled direct to the PLC as those with a transmitter installed on the RTD. But I have had customers require the transmitter and have it connected within 6 inches of the RTD, just so the run back to the PLC is in shielded cable. This is a good precaution. Pharmaceutical companies are very likely to require the transmitter to get the shielded cable, as they are extremely nervous about losing a batch of what ever the process skid is making. __________________ They asked me if I was all right - I said, "well, no, I am half left."
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