I believe schlebda's question actually raised 2 points
1st, "Is there an industry standard or performance expectation for 2 wire 4-20mA output devices (actuators, positioners) for signal levels below 4mA?"
This answered by Postdanw2, Yes, there is a Standard laid down by NAMUR and Nearly all...
The ability of a magflo meter to measure flows in partially filled pipes is heavily dependent on the design of the coils in relationship to the pickup electrodes.
I only have limited experience on actual applications, but believe that the Toshiba make a specific meter for this application that...
I agree with Roydm/LJseagull, but remember that if you use a wet leg reference (figure A3)on the HP and connect the LP to the stack, the output of the transmitter will be inverse to the level.
I trust this helps,
Mlv
http://www.coulton.com
Jim,
I am unsure how you come to a SG of 0.667 At 115 Barg in the drum.
The "water" in a steam drum is actually a bubbling mix of water and steam. The density of which is totally unpredictable and changing as steam bubles are released off the tubes in an uncontrolled manner.
To add to the...
Sorry,
I had assumed that we we talking in general terms about splitting a 4-20mA loop.
To implement this technique within a control loop the diagram would be modified as per the attached.
Thanks Roy for preventing further confusion.
I trust this helps,
Mlv...
The lowest cost option is to wire the control valve and the PLC in series with the transmitter 4-20mA loop
There are two issues to watch out for:-
1. That the total loop resistance remains less than 600 Ohms.(which shouldn't be difficult)
2. Wire the PLC in the loop after the valve positioner...
If there is a 3 valve manifold fitted to the transmitter then the increase in temperature could be due to the equaliser valve not seating correctly.
I suggest that you isolate the transmitter at the 3 valve manifold and attempt to ensure there is no flow through the impulse lines.
Roy may be...
I agree with Roy that the issue is the the density of the water in the drum. The article that Roy refers to is very useful and confirms my suggestion that balancing the steam flow against the water flow should be used as the primary measure for level control (see figure 2 in the Tyco article. In...
A simple transfer block with a digital flag from a Bialey DCS, will not normally product a mA output . So if your "elctro pneumatic acutator" is actually an electro pneumatic valve positioner. Then you will not have achieved anything.
I accept that if your "elctro pneumatic acutator" has a...
I apreciate that experience often leads us to make rational decisions, but my experience of current time of flight and even dopplar devices is that modern devices are head and shoulders above similar technology of 5 yrs ago. so my opinion has changed with time.
I would suggest hiring a trial...
The answer is, .... two wires.
However it would be good to know what you meant by "elctro pneumatic acutator" as this could be loosely interpreted as a solenoid (on off in nature), or e/p positioner (modulating in nature)
If it is the former, then you will need a relay output from the DCS...
IS by definition stated that the components within the enclosure do not store enough energy to cause ignition. Adding extra cable entries does not effect the IS rating.
I trust this helps,
Mlv
http://www.coulton.com
I do not accept the argument that DP transmitters have a problem with pressure. For example the Fuji Electric FCX series transmitter is now capable to operate with a static pressure of 1035 Barg without adverse effects on the accuracy.
I believe that the issue is a function of definition. The...
I guess that what we are all trying to achieve is getting a true measurement from the transmitter?
I agree that manufacturer calibration equipment is at least one order of magnitude more accurate than any local site standard. But the manufacturer is unable to predict installation effects. These...
