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Why 250mA fuse for 4-20mA analog input?
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Many 4-20 mA transmitters will pull 25 mA in the event of an internal fault, or if a seriously...
Power factor in electrical generation systems
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In an electric motor, the torque is developed by the interaction between the stator current and a...
Steam flow through a valve
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It depends on the valve characteristic - for a typical large turbine, the curve of flow vs opening...
Temperature compensation for density variation of air in hydrostatic measurement
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It also undergoes a fairly rapid change in temperature if the machine is filled with cold water and...
FWIW ...
I recently dismantled a discarded washing machine, mainly to get at the motor for use...
what is the minimum requirements for junction box in zone 0?
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The only requirements in IEC60079.11 relating to enclosure design refer to Ingress Protection. As...
Learning about different aspects of automation and gaps in learning
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Profibus is a very minor technique in a very large field - I am also 66+ and have never come...
Question about how a PID Controller might be implemented in C++. How to go from continuous to discrete signal in C++?
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First you need to take samples of the value to be controlled at finite intervals - the calculation...
When are IS barriers required?
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You always need some sort of energy limiter (barrier or isolator) between powered equipment and a...
Who is responsible for risk?
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Only the final end-user can do a full risk assessment, taking into account things like the...
Error of proportional only controller
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A mathematical model of the controller is very easy - the output is proportional to the offset. In...
The "error from the setpoint" IS the offset....
You can ESTIMATE the offset (not calculate it precisely) if you realise that the proportional band...
AC generator voltage,excitation current, voltage drop and power flow
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> But this makes me think that the VARS out of the generator could be controlled by the...
Now you've got me thinking ...
You're on the right track with your mental model. Unfortunately,...
There is a phenomenon in electrical systems called reactance. This applies to AC-only systems, and...
Safety risk assessment report
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This raises another point often overlooked during development of a safety system.. You need to...
I think the size of the team involved depends on the circumstances. For a new plant where a...
A very broad-brush approach would start with the following headings:
. What could go wrong? -...
Most successful HMI design of all time.
Contradictory trend in HMI design? You tell me.
Contradictory trend in HMI design? You tell me.
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The problem with gratuitous moving, flickering, flashing etc is that it can interfere with the...
What is the error if you use a Tx cable with a K thermocouple?
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I can quite believe it - especially if the guy responsible for the original design is now...
Yep - there are two extremes.
If the terminals in the thermocouple head are at more or less the...
The best way to make an estimate of the error is to set up a test system - stick a Type K in a bath...
Type T will have one leg of copper - which is copper-coloured ......
Should one perform a formal safety risk assessment?
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Check out the ALARP** principle - this indicates that there is formal recognition of the need to...
Looking to determine AVR and generator response during islanding of site from National Grid.
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The actual behaviour when islanded will depend on what is used as set-point and PV for the AVRs. ...
How can I resist a challenge like that! Some further information would be useful -
- what is...
from the Forum department...
Running Serial Modbus and TCP Modbus on the same computer simultaneouslyCan there be an issue with running Serial modbus and TCP modbus on the same computer at the same time if some of the addresses are the same?
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As long as the receiving computer can distinguish between the target hardware items, the addresses...
Are most automation equipment broken down into finite state machine logic?
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According to IEC61131 Table 46, there are three variants on the divergence of sequence. All three...
An SFC is made up of transitions and actions - a check for a particular result will trigger a...
I find that using an SFC approach to the design stage of a complex sequence can highlight all the...
Process of selecting Control Valves & DCS settings
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CV is a constant relating the flow through a control valve to the pressure drop across it. The...
What is the best approach to control a VFD pump speed in order to keep both a minimum pressure and a minimum flow in the distribution loop?
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You can quite safely operate a selective control scheme with both pressure and flow controllers. As...
EEx ia and EEx [ia] and [EEx ia] and isolation barrier
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The first thing is that you need to find out exactly what specific codes and standards are...
Why the load angle of the alternator is kept low (20-40 degree)?
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If the angle goes over 90 degrees you have a problem - and pole slipping will result. Since there...
Can anyone tell me what difference between EEx ia and EEx [ia] and [EEx ia]?
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Hi Bolter,
An Ex e enclosure doesn't change the risk of ignition in any way - the atmosphere can...
Connecting flame proof device EEX d (faure herman ultrasonic transmitter) to an intrinsically safe system
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Hi Rashid,
Since the isolator will be located inside the dust-excluding enclosure, it will not...
Hi Rashid,
The situation you are describing seems quite complex - and is getting well away from...
Hi Rashid,
As I interpret your situation, the instruments which are rated Ex d [ia] IIC will...
If the sensor is Ex d with no other designation, then the associated circuits will not be IS...
how to calculate the pole position?
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See my reply to your latest post on thread http://www.control.com/thread/1351224915#1351654329...
Conversion of torque into amps
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You asked for it ... I've also had a look at your post about pole position detection, and will have...
Hi Chandru,
I take a slightly different approach to these things than CSA, so you might find my...
What is the zone classification for a sensor installed on the fuel transfer line?
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Hi Kamath,
The right question to ask is - "Is the switch a possible source of...
intrinsically safe for simple apparatus
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Simple answer - yes.
A simple device, by definition, is one that cannot generate more than 1.5...
We have a fabricator to whom we have paid millions of dollars who refuses to turn over any logic diagrams, ladder logic, HMI, etc., claiming it to be proprietary.
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If the logic has safety implications, then the site owner/operator probably (depending on legal...
Zone 2 terminal box
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In general, I'd say yes. You will need to check the compliance documents for the terminals for...
Need help on how multiple PID loops can be interconnected
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This is a situation where selective control can help. Basically, you want to use the temperature...
A breaker on the electrical diagram, as tripped or OK?
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Aaahhh ... but what do you mean by "normal"? That's the problem.
An electrician...
Let me know about 4-20mA through EExi-barriers (Intrensically safe signals).
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Ex i is used to prevent a low-power electrical circuit from igniting a flammable atmosphere. It...
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