N
Neo
CSA,
You said "I think the important thing to get out of this exercise is how to "read" signal names and
logic (rungs)."
Ok, i will keep this in my mind.
------------------------------------------------------------------------------------------------------
I'm still confused about the concept of inversion masking.
You said "So, GE's answer to ensuring that circuits are in good condition (before there was even
contact supervision available in any programmable control system) was to "invert" the input."
Just take the signal l26qn for example, the temperature switch contact is closed(logic 1) under normal operating circumstances,and when the circuit fails, l26qn will turn to logic 0. So, it has
the function of circuit supervision.
So why inversion masking.
As the same to signal l12hblt,if the circuit fails,it will become logic 0.
Again why should the l12hblt be inverted.
"GE decided decades ago to standardize on circuits that were closed under normal operating
circumstances, and opened to alarm or trip the turbine."
Does that mean logic 1 refers to normal operating circumstance, and logic 0 to alarm or trip the turbine.
"For example, if you went to the VCRC input where 26QN-1 is connected, you would see the input is NOT inverted (it's "Normal").
How is one signal inverted,in hardware way or software way. If it is in software one, a signal can be inverted like this:<pre>
prestate poststate
( )---------|/|-------( )</pre>
------------------------------------------------------------------------------------------------------
"You asked why this input is not inverted, but l12hblt is inverted. The input could have been inverted, and it would work just fine. Of course, the "signal name" would be exactly opposite of what it should be because it would be a logic "1" when the L.O. Tank temperature was less than normal. Sometimes these things,even though they could go one way or the other (with a signal name change to make it easier) are just continued for decades--and this is one of them."
I am confused about "sigal name",the name of signal? If does mean name of signal, i think whether or not the signal is inverted, is has no effect on signal name,just a name.
So, this confuses me .
------------------------------------------------------------------------------------------------------
In one reply, i typed one rung below:<pre>
L45FP_STCK L3STCK
---.....------|/|---------() </pre>
The contact sense of L45FP_STCK is typed wrong,Which should be:<pre>
L45FP_STCK L3STCK
---.....------||---------()</pre>
You found that mistake,and deduced that either an incorrectly chosen name or the contact sense is typed wrong.
How did deduce it?
And you said the signal name indicates this signal will be a logic "1" when the fire protection circuit is ready to detect a fire.
How did you know it is a logic "1" not a logic "0" when the fire protection circuit is ready to detect a fire?
Those are the questions bother me a lot, and maybe it is good to deal those questions right now.And i hope it will not bother you too much as some of them are silly.
------------------------------------------------------------------------------------------------------
<pre>
L86CB L4Y L3BHSTCK L30CC_STCK l33cl1 l45fp1 l27f L2STCK2
--------|/|-------||---------||---------|/|------|/|-------|/|-----|/|--------( )
| |
| true |
--------------------</pre>
L86CB = Surge protection trouble startup lockout;
L3BHSTCK = Comp operating limit BH start check perm logic;
L30CC_STCK = Fire protection trouble-GT start inhibited;
l33cl1 = Fire protection aux/turb/laod compt CO2 locked;
l45fp1 = Fire protection aux/turb/laod compt fire pre-detec;
l27f = Fire protection trip relay undervoltage;
I will examine this rung next time.
Best regards
Neo
You said "I think the important thing to get out of this exercise is how to "read" signal names and
logic (rungs)."
Ok, i will keep this in my mind.
------------------------------------------------------------------------------------------------------
I'm still confused about the concept of inversion masking.
You said "So, GE's answer to ensuring that circuits are in good condition (before there was even
contact supervision available in any programmable control system) was to "invert" the input."
Just take the signal l26qn for example, the temperature switch contact is closed(logic 1) under normal operating circumstances,and when the circuit fails, l26qn will turn to logic 0. So, it has
the function of circuit supervision.
So why inversion masking.
As the same to signal l12hblt,if the circuit fails,it will become logic 0.
Again why should the l12hblt be inverted.
"GE decided decades ago to standardize on circuits that were closed under normal operating
circumstances, and opened to alarm or trip the turbine."
Does that mean logic 1 refers to normal operating circumstance, and logic 0 to alarm or trip the turbine.
"For example, if you went to the VCRC input where 26QN-1 is connected, you would see the input is NOT inverted (it's "Normal").
How is one signal inverted,in hardware way or software way. If it is in software one, a signal can be inverted like this:<pre>
prestate poststate
( )---------|/|-------( )</pre>
------------------------------------------------------------------------------------------------------
"You asked why this input is not inverted, but l12hblt is inverted. The input could have been inverted, and it would work just fine. Of course, the "signal name" would be exactly opposite of what it should be because it would be a logic "1" when the L.O. Tank temperature was less than normal. Sometimes these things,even though they could go one way or the other (with a signal name change to make it easier) are just continued for decades--and this is one of them."
I am confused about "sigal name",the name of signal? If does mean name of signal, i think whether or not the signal is inverted, is has no effect on signal name,just a name.
So, this confuses me .
------------------------------------------------------------------------------------------------------
In one reply, i typed one rung below:<pre>
L45FP_STCK L3STCK
---.....------|/|---------() </pre>
The contact sense of L45FP_STCK is typed wrong,Which should be:<pre>
L45FP_STCK L3STCK
---.....------||---------()</pre>
You found that mistake,and deduced that either an incorrectly chosen name or the contact sense is typed wrong.
How did deduce it?
And you said the signal name indicates this signal will be a logic "1" when the fire protection circuit is ready to detect a fire.
How did you know it is a logic "1" not a logic "0" when the fire protection circuit is ready to detect a fire?
Those are the questions bother me a lot, and maybe it is good to deal those questions right now.And i hope it will not bother you too much as some of them are silly.
------------------------------------------------------------------------------------------------------
<pre>
L86CB L4Y L3BHSTCK L30CC_STCK l33cl1 l45fp1 l27f L2STCK2
--------|/|-------||---------||---------|/|------|/|-------|/|-----|/|--------( )
| |
| true |
--------------------</pre>
L86CB = Surge protection trouble startup lockout;
L3BHSTCK = Comp operating limit BH start check perm logic;
L30CC_STCK = Fire protection trouble-GT start inhibited;
l33cl1 = Fire protection aux/turb/laod compt CO2 locked;
l45fp1 = Fire protection aux/turb/laod compt fire pre-detec;
l27f = Fire protection trip relay undervoltage;
I will examine this rung next time.
Best regards
Neo