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Went through logic for test addition

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Robin Clark 2010-11-06 12:11:58 +00:00
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94
fmmd_design_aide/fmmd_design_aide.tex
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@ -216,7 +216,7 @@ We could detect the effect on the reading with the potential divider
according to the following formula.
%% check figures
The potential divider is now $\frac{820R+820R}{2M2+820R+820R}$ over 5V this gives
The potential divider is now $\frac{820R+820R}{2M2+820R+820R}$ over 5V ci this gives
3.724mV, amplified by 184 this is 0.685V \adcten{140}.
%
The potential divider with the second resistor
@ -257,9 +257,9 @@ can be switched on to apply the test parallel resistance, and
off to obtain the correct reading.
%
We must examine each test case from these two perspectives.
For TEST LINE ON the transistor is turned OFF
For $\overline{TEST\_LINE}$ ON the transistor is turned OFF
and we are in a test mode and expect the reading to go up by around \adcten{70}.
For TEST LINE OFF the tranistor is on and R36 is by-passed,
For $\overline{TEST\_LINE}$ OFF the tranistor is on and R36 is by-passed,
and the reading is assumed to be valid.
\begin{table}[h+]
@ -272,21 +272,91 @@ and the reading is assumed to be valid.
% R & wire & res + & res - & description
\hline
\hline
%% OK TR1 OFF
TEST LINE ON & TC:1 $R36$ SHORT & No added resistance & NO TEST EFFECT & XX 1.38 \\ \hline
TEST LINE OFF & TC:1 $R36$ SHORT & dormant fault & NO SYMPTOM & XX 1.38 \\ \hline
TEST LINE ON & TC:2 $R36$ OPEN & open circuit & OPEN CIRCUIT & XX 12.42\\ \hline
TEST LINE OFF & TC:2 $R36$ OPEN & open circuit & OPEN CIRCUIT & XX 12.42\\ \hline
%% OK TR1 OFF , and so 36 in series. R36 has shorted so
$\overline{TEST\_LINE}$ ON & TC:1 $R36$ SHORT & No added resistance & NO TEST EFFECT & XX 1.38 \\ \hline
%%
$\overline{TEST\_LINE}$ OFF & TC:1 $R36$ SHORT & dormant failure & NO SYMPTOM & XX 1.38 \\ \hline
%% here TR1 should be OFF, as R36 is open we now have an open circuit
$\overline{TEST\_LINE}$ ON & TC:2 $R36$ OPEN & open circuit & OPEN CIRCUIT & XX 12.42\\ \hline
%% here TR1 should be ON and R36 by-passed, the fact it has gone OPEN means no symptom here, a dormant failure.
$\overline{TEST\_LINE}$ OFF & TC:2 $R36$ OPEN & dormant failure & NO SYMPTOM & XX 12.42\\ \hline
\hline
TEST LINE ON & TC:3 $TR1$ ALWAYS ON & dormant fault & NO SYMPTOM & XX 1.38 \\ \hline
TEST LINE OFF & TC:3 $TR1$ ALWAYS ON & No added resistance & NO TEST EFFECT & XX 1.38 \\ \hline
TEST LINE ON & TC:4 $TR1$ ALWAYS OFF & resistance added failure & NO TEST EFFECT & XX 1.38 \\ \hline
TEST LINE OFF & TC:4 $TR1$ ALWAYS OFF & dormant fault & NO SYMPTOM & XX 1.38 \\ \hline
%
%% TR1 OFF so R36 should be in series. Because TR1 is ON because it is faulty, R36 is not in series
$\overline{TEST\_LINE}$ LINE ON & TC:3 $TR1$ ALWAYS ON & No added resistance & NO TEST EFFECT & XX 1.38 \\ \hline
%%
%% TR1 ON R36 should be bypassed by TR1, and it is, but as TR1 is always on we have a dormant failure.
$\overline{TEST\_LINE}$ OFF & TC:3 $TR1$ ALWAYS ON & dormant failure & NO SYMPTOM & XX 1.38 \\ \hline
%%
%% TR1 should be off as overline{TEST\_LINE}$ is ON. As TR1 is faulty it is always off and we have a dormant failure.
$\overline{TEST\_LINE}$ LINE ON & TC:4 $TR1$ ALWAYS OFF & dormant failure & NO SYMPTOM & XX 1.38 \\ \hline
%%
%% TR1 should be ON, but is off due to TR1 failure. The resistance R36 will always be in series therefore
$\overline{TEST\_LINE}$ OFF & TC:4 $TR1$ ALWAYS OFF & resistance always added & NO TEST EFFECT & XX 1.38 \\ \hline
\hline
\end{tabular}
\label{tab:testaddition}
\end{table}
\subsection{Test Cases Analysis in detail}
The purpose of this circuit is to switch a resistance in when we want to test the circuit
and to switch it out for normal operation.
The control is provided by a line called $\overline{TEST\_LINE}$.
Thus to apply the test conditions we set $\overline{TEST\_LINE}$ to OFF or false
and to order normal operation we set it to ON or true.
\subsubsection{TC 1}
This test case looks at the shorted resistor failure mode of R36.
\paragraph{$\overline{TEST\_LINE}$ ON}
Here TR1 should be off and R36 should be in series. As R36 is shorted, this means that
no resistance will be contributed to the circuit by R36.
In the terms of the behaviour
of the functional group, this means that it will provide no test effect.
\paragraph{$\overline{TEST\_LINE}$ OFF}
Here TR1 will be on and by-pass R36, so it does not make any difference if
R36 is shorted. This is a dormant failure, we can only detect this failure
when $\overline{TEST\_LINE}$ is ON.
\subsubsection{TC 2}
This test case looks at the open circuit resistor failure mode of R36.
\paragraph{$\overline{TEST\_LINE}$ ON}
Here TR1 should be off and R36 should be in series. As R36 is open, this means that
the test circuit is no open.
In the terms of the behaviour
of the functional group, this means that it will cause an open circuit failure.
\paragraph{$\overline{TEST\_LINE}$ OFF}
Here TR1 will be on and by-pass R36, so it does not make any difference if
R36 is open. This is a dormant failure, we can only detect this failure
when $\overline{TEST\_LINE}$ is ON.
\subsubsection{TC 3}
This test case looks at the transistor failure mode where TR1 is always ON.
\footnote{The transistor is being used as a switch, and so we can model it as having two failure modes ALWAYS ON or ALWAYS OFF.}
\paragraph{$\overline{TEST\_LINE}$ ON}
Here TR1 should be off and R36 should be in series. As TR1 is always ON, this means that
R36 will always be by-passed. Thus there will be no test effect.
\paragraph{$\overline{TEST\_LINE}$ OFF}
Here TR1 should be on and by-pass R36.
This is a dormant failure, we can only detect this failure
when $\overline{TEST\_LINE}$ is ON.
\subsubsection{TC 4}
This test case looks at the transistor failure mode where TR1 is always OFF.
\paragraph{$\overline{TEST\_LINE}$ ON}
Here TR1 should be OFF and R36 should be in series.
This is a dormant failure, we can only detect this failure
\paragraph{$\overline{TEST\_LINE}$ OFF}
Here TR1 should be ON, but is OFF due to failure.
The resistance R36 will always be in series.
As a symptom for this circuit, it means that there would be no test effect.
\subsection{conclusion of FMMD analysis on safety addition}
For the FMMD analysis in table \ref{tab:testaddition} we have two failure modes for its derived component
`no~test~effect' or `open~circuit'.
%~out~of~range'.