Issues with valve position feedback using a HART smart valve actuator?
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It is said that there are three ways for an intelligent valve positioner to determine the opening degree of the on-site control valve: 1. Adding a 4–20mA signal sent by the valve position transmitter to provide feedback on the valve position; 2. Using the intelligent valve position transmitter to send a 4–20mA signal for valve position feedback via two wires; 3. Utilizing the HART function of an HART-enabled intelligent valve positioner to read the valve position, which requires the cooperation of a DCS. Are these statements correct? Question: 1. Is there a dedicated valve position transmitter? Are the so-called valve position transmitters simply feedback modules added to valve positioners? 2. Does a smart valve position transmitter necessarily require a separate two-wire connection (different from the two wires used by the DCS to control the valve) to transmit the 4–20 mA signal indicating the valve position? Along with the wires used for controlling the valve, are four wires needed in total? 3. How can the valve position be read using HART with a HART intelligent valve positioner? Can it be read via a handheld operator? How does DCS read it? Is a special safety barrier required, a special input card, or is nothing needed at all – just configuration settings?
There is a separate valve position transmitter, which is quite common. An intelligent locator with a Hart module cannot accurately perform the function of transmitting valve position on its own. However, some intelligent positioners can be equipped with an optional valve position transmitter, that is, it can be integrated inside the positioner. Even when integrated internally, the valve position loosening function operates as a separate two-wire system.
Answer: 1. Both are available; differences may exist depending on the manufacturer. 2. It is two separate wires; with the valve transmitter, there are four wires in total. 3. The DCS card must be capable of supporting the HART protocol, enabling the extraction of HART signals from 4–20 mA signals for use in DCS configuration.
This post was last edited by 49205455 on 2015-11-9 at 21:49. 1 pair, unless the valve comes with it already from the factory. It seems that only Emerson’s DELTAV models have this feature in the 2-to-3 configuration; moreover, a license has to be purchased for it. So, unless your company uses DELTAV systems and has already acquired the license needed to use the Hart function, it’s better to simply buy a feedback device and a transmitter. You need to know how expensive Emerson’s products are – a single battery can cost you 8,000, while the feedback devices don’t cost much at all. Hehe.
We use Siemens valve positioners here; if feedback is required, an additional module must be added, to which the feedback signal wires are connected. Therefore, the valve positioners we use that transmit signals are of the four-wire type.