DCS for on-site instrument diagnosis
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The tender requires the DCS to implement an instrument management system; this function is usually handled by a fieldbus-based DCS. However, the DCS is also required to be able to receive two-wire signals from instruments – can a DCS therefore have both a fieldbus design and a hardwired design?
HART is a high-frequency signal superimposed on 4–20mA. Ask Emerson or Siemens whether the bus signals are the same as well. If that’s the case, use a setup with one input and two outputs: one connected to a 4–20mA input card and the other to the bus, and that’s it. If that doesn’t work, use HART as the bus to trick those who pose difficult questions: lol
The cost of using a full bus is very high, especially for things like actuators
This post was last edited by pH7 on 2011-4-11 09:42. Personally, I think the HART bus meets the requirements you mentioned.
Most imported DCS systems these days can achieve this function. The common practice is for field instruments to support digital communication, either via HART or fieldbuses. The I/O modules of DCS systems have communication capabilities, and device management software, such as Emerson’s device management software, must be embedded in the DCS.
Fieldbus instruments are different from ordinary smart instruments that have features such as HART communication, and there is a significant price difference between the two. A fully fieldbus-based DCS can be implemented, but such a DCS requires the ability to receive two-wire signals from instruments; I’m curious to know what the reasoning behind this is