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Supplying 24VDC field power to an instrument

Hello, i am planning to install an Endress and Hauser Gas Flow Switch to an IS DI Namur Charm, however the instrument requires constant power between 18-30 VDC (Not loop powered). On the S Series installation manual I can see that the switched output signal of my instrument connects to terminals 3 and 4 of my IS Charm terminal block, but I want to be sure that I can supply field power via terminals 1 and 2. Also my instrument requires approximately 3.0 watts of power, and I want to be sure the IS charm terminal block can supply this. Am I also correct in assuming that no barrier is required to supply this power to the hazardous area ? I am new to DeltaV hardware, so I apologise if this is an obvious question. Many thanks. Aidan 

• fieldpower
• Endress
• ischarm

Aidan Fusco

• 16 Nov 2020 8:48 PM
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6 Replies

• Gary Law

  

  • 17 Nov 2020 2:23 PM

  18V is well above the 8V that is specified for the CHARM
  Also the CHARM is designed to power the sensor , and what you are describing is a 3 or 4 wire connection.
  This is NOT a suitable installation.

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• Aidan Fusco

  

  • 17 Nov 2020 5:59 PM

  In reply to Gary Law:

  Hello Gary, thanks for taking the time to reply to my query. I had concerns that this particular type of charm would be unable to supply the field power required. Excuse my lack of knowledge on the S series hardware, but what are terminals 1 & 2 on the IS charm terminal block for ? Are they field power connections, but in this case limited to 8v due to its Namur characteristics? I have a 24v power supply available in the charms cabinet that is being used to power the CIOC card, however if I use this I would have to use an additional barrier to supply 24vdc to the instrument in the field. Thanks, Aidan.

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• Gary Law

  

  • 18 Nov 2020 2:08 PM

  In reply to Aidan Fusco:

  BOL and the product Data Sheet both indicate these terminals are unused for this CHARM type.
  They would be used for the RTD for example.
  Note this CHARM type is NOT designed for a 3 or 4 wire connection , so unless the Device is a 4 wire device that acts like a standard NAMUR proximity switch, I think you will have issues.

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• Aidan Fusco

  

  • 18 Nov 2020 4:11 PM

  In reply to Gary Law:

  Hi Gary, I didn't understand that terminals 1 and 2 were unused for this Charm type, I thought the example was showing it's configuration for 2 wire device, either a Namur sensor, or a contact on a switch for example. Am I correct in saying that in IS Marshalling there is no DI Charm type suitable for supplying a device with field power of +24VDC ? I saw in the Non-IS marshalling hardware that there is a 24VDC power charm that can be used, which is unfortunately not shown as an option for IS Charms. Thanks, Aidan.

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• Andre Dicaire

  

  • 18 Nov 2020 4:53 PM

  In reply to Aidan Fusco:

  The non-IS CHARM Baseplates provide an Injected Power option that provides 24 V field power for use in three and four wire devices, and is used by the Power CHARM to provide fused 24 V power to a field device. The IS baseplates do not allow this as all field side wiring is IS, is current limited and isolated.
  
  Would an IS DO CHARM act as a power source to provide power to the device? No, that would not work. Apart from the IS DO being rated for 11 Volts at 45 mA, it is isolated from the DI circuit, and you would be in "unsupported" Territory.
  
  Your best bet is to look at a separate IS solution for this device. Either a barrier for the Power circuit and the IS DI CHARM for signal, or a Barrier for both that provides a safe DI signal to a standard DI channel.

  Andre Dicaire

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• Aidan Fusco

  

  • 18 Nov 2020 7:36 PM

  In reply to Andre Dicaire:

  Hello Andre, many thanks for taking the time to reply to my post. From the information you have provided above it looks like a separate 24VDC supply used in conjunction with a barrier for the power circuit to my instrument is the best option.

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