Right, Yes it is the pressure transmitter the one that measures the pressure in the test cell or what ever you call it. The scaled analog is the conversion of the raw analog value (you may not need this if the PLC has an analogue card settings as many do now) if not then the analog is presented as a number 0-4096 (or what ever is the range)
The first two rubgs is just a way of converting the raw integer of 0-4096 into a pressure i.e. 0.00-500.00 PSI or what eber is the range it could be bar, ior inches water gauge, it is so the operator can see it working in actual real values not just a number.
so that is questions 1 & 2
3. they are not if you look there is a little R inside the coil this means reset it, this is a set/reset of a bit when for example the rung that checks the pressure if out of tollerance we set the alarm bit, if we only used it as a normal coil then when it goes off this step it will go off so we latch it to display the message & only de-latch it on a start of a new test.
4. The e-stop is usually a hard wired Normally closed to a safety relay that drops out the power to any outputs from the PLC that drive any equipment that could be considered dangerous to persons, it has a spare contact that also goes to a PLC input, should someone press the e-stop it cuts power to motors or other moving equipment as well as being used in the plc to reset the process back to idle so when the e-stop is re-instated it does not start automatically this is generally always a N/C so the PLC input s on, & goes off when pressed, should the wire come off the feed to this switch then it will turn off the input & the plc will see it as a stop condition, if you used N/O switches then if the power feed to a switch was lost then the system will continue to run if the button is pressed.
5. The idea of an inflight is that often after stopping a pump or what ever, there continues to be in this case a rise in pressure as it takes time to stop a pump or close a valve, the idea is to predict it takes 1 second to close, the valve or pump stopping/closing will still be producing flow so if you stop a pump at say 2 psi before the setpoint reachedc the natural delay in stopping the pump will add another 2 PSI to the pressure, like when you see a red traffic light, if you waited to brake till you were at the lights by the time you stopped you have past the white line or hit a car comming across the junction, this can be set at commissioning it could turn out to be 0 or very small depending on how fast the pressure increases.
6. It is not, The shut off valve is Normally open & you energise it to close it, this is a safety feature so that the pressure cannot build up if the process is running, often this has it's feed from a plc output via a contact on the safety relay & possibly some electric bolt operated lid on the test vessel so the operator cannot try to open it while pressurised.
7. This is the point when the value of the analog output is changed from perhaps 100% to say 20% i.e. slow build up of pressure so that you can get closer to the setpoint it's like again, driving towards traffic lights if they are red you start reducing your speed before you get there so you do not overrun.
8 that is to stop the decrementing of the raw analog below 0 (actually I set it to 10 as we decrement by 10 every 100ms) the idea is it will never go below 0 as this is only simulation logic it will not be needed so can be deleted when tested on simulation.
9 What this does is the original stored pressure at the test start could possibly drop by a very small amount even 0.000001 psi (probably due to noise on the analog signal) so if for example the pressure was at 200.0200 at start of test & at the end the reading was 200.001.0 then it would fail the test so what we are doing is just having a bit of a band to allow for fluctuations, remember earlier I said when comparing one value with another in floating point you will never get it exact, there are minor erros in floating point maths that can accumulate the more maths that is processed.
10 That is to check the pressure has fallen to below a reasonable level so the sequence can step on back to idle so the operator knows it's safe to open the pressure vessel or what ever it is.
Ooppsss may have got the numbers mixed up with the rung numbers will have to stop here the other half wants her cup of tea, will try to visit tomorrow. but it should give you a starting point.
The first two rubgs is just a way of converting the raw integer of 0-4096 into a pressure i.e. 0.00-500.00 PSI or what eber is the range it could be bar, ior inches water gauge, it is so the operator can see it working in actual real values not just a number.
so that is questions 1 & 2
3. they are not if you look there is a little R inside the coil this means reset it, this is a set/reset of a bit when for example the rung that checks the pressure if out of tollerance we set the alarm bit, if we only used it as a normal coil then when it goes off this step it will go off so we latch it to display the message & only de-latch it on a start of a new test.
4. The e-stop is usually a hard wired Normally closed to a safety relay that drops out the power to any outputs from the PLC that drive any equipment that could be considered dangerous to persons, it has a spare contact that also goes to a PLC input, should someone press the e-stop it cuts power to motors or other moving equipment as well as being used in the plc to reset the process back to idle so when the e-stop is re-instated it does not start automatically this is generally always a N/C so the PLC input s on, & goes off when pressed, should the wire come off the feed to this switch then it will turn off the input & the plc will see it as a stop condition, if you used N/O switches then if the power feed to a switch was lost then the system will continue to run if the button is pressed.
5. The idea of an inflight is that often after stopping a pump or what ever, there continues to be in this case a rise in pressure as it takes time to stop a pump or close a valve, the idea is to predict it takes 1 second to close, the valve or pump stopping/closing will still be producing flow so if you stop a pump at say 2 psi before the setpoint reachedc the natural delay in stopping the pump will add another 2 PSI to the pressure, like when you see a red traffic light, if you waited to brake till you were at the lights by the time you stopped you have past the white line or hit a car comming across the junction, this can be set at commissioning it could turn out to be 0 or very small depending on how fast the pressure increases.
6. It is not, The shut off valve is Normally open & you energise it to close it, this is a safety feature so that the pressure cannot build up if the process is running, often this has it's feed from a plc output via a contact on the safety relay & possibly some electric bolt operated lid on the test vessel so the operator cannot try to open it while pressurised.
7. This is the point when the value of the analog output is changed from perhaps 100% to say 20% i.e. slow build up of pressure so that you can get closer to the setpoint it's like again, driving towards traffic lights if they are red you start reducing your speed before you get there so you do not overrun.
8 that is to stop the decrementing of the raw analog below 0 (actually I set it to 10 as we decrement by 10 every 100ms) the idea is it will never go below 0 as this is only simulation logic it will not be needed so can be deleted when tested on simulation.
9 What this does is the original stored pressure at the test start could possibly drop by a very small amount even 0.000001 psi (probably due to noise on the analog signal) so if for example the pressure was at 200.0200 at start of test & at the end the reading was 200.001.0 then it would fail the test so what we are doing is just having a bit of a band to allow for fluctuations, remember earlier I said when comparing one value with another in floating point you will never get it exact, there are minor erros in floating point maths that can accumulate the more maths that is processed.
10 That is to check the pressure has fallen to below a reasonable level so the sequence can step on back to idle so the operator knows it's safe to open the pressure vessel or what ever it is.
Ooppsss may have got the numbers mixed up with the rung numbers will have to stop here the other half wants her cup of tea, will try to visit tomorrow. but it should give you a starting point.