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Old September 14th, 2018, 12:24 PM   #1
Snyd1
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1734-IR2 and IT2I

Anyone that has these thermocouple or RTD cards in use answer a question I have.

Reading the manual they show low scaling endpoint at freezing 0c (32F). My question: does that mean they will not register temperatures below freezing?
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Old September 14th, 2018, 06:45 PM   #2
Mike Lamond
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You're looking at the table for custom input scaling. That only applies if your application doesn't use temperature inputs. For the usable temperature ranges of each TC and RTD type, go back two pages to the Supported Sensor Types tables.
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Old September 17th, 2018, 09:39 AM   #3
Snyd1
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Thanks completely over looked that. What exactly is the benefit of using one of the specialty cards over a regular analog input and SCP instructions to scale the signal?

Last edited by Snyd1; September 17th, 2018 at 09:41 AM. Reason: Monday morning
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Old September 17th, 2018, 08:43 PM   #4
Mike Lamond
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The biggest benefit is eliminating RTD or TC transmitters. One of my recent projects had over 450 RTD sensors and head mounted transmitters weren't an option. Using TTs and 8 channel current inputs would have doubled or tripled the size of the remote I/O panels.


There are some negatives to consider: The 1734-IR2 modules have a high backplane current draw, limiting them to three on the adapter and five per expansion power supply. With communication limits, there's a practical limit of 18 modules per Ethernet node. Each adapter and module require a CIP connection to the processor. We used almost half of the 512 connections available in an L72 processor.
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Old September 17th, 2018, 08:58 PM   #5
Ken Roach
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An ordinary analog card is built for a different voltage or signal range, with A/D converters of different precision and range, and different protective circuitry.

The 1734-IT2I has a sensitivity of 2.5 microvolts per count, while the 1734-IE2V has a sensitivity of 320 microvolts/count.

And ordinary analog modules don't have the onboard non-linear scaling lookup tables that are standard for thermocouples (in the case of the -IT2).

Another drawback to using sensitive input circuits is that they're generally delicate. Connect 24V DC to a thermocouple input module and you will damage it.

But the fact that I can connect a Cold-Junction Compensator to the module (another specific feature of the Thermocouple module) and get an accurate value of temperature in tenths of a degree is a big benefit to simplification of my programming and HMI.
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