<p style="text-align:justify"><span style="font-size:14px">The two-input relays can be classified as:</span></p>

<ul>
	<li style="text-align:justify">
	<p><span style="font-size:14px">An Amplitude Comparator</span></p>
	</li>
	<li style="text-align:justify">
	<p><span style="font-size:14px">A Phase Comparator</span></p>
	</li>
</ul>

<ol>
	<li style="text-align:justify">
	<p><span style="font-size:14px">An Amplitude Comparator: A two-input comparator relay which compares the magnitudes of two quantities irrespective of their phase relations is known as an amplitude comparator. A two-input relay which compares the phase angle between two quantities irrespective of their magnitudes is known as a phase comparator.</span></p>
	</li>
</ol>

<p style="margin-left:24px; text-align:justify"><span style="font-size:14px">A and B are two electrical quantities. If an amplitude comparator relay is used,</span></p>

<ul>
	<li style="text-align:justify">
	<p><span style="font-size:14px">If |A| = |B|, the relay is under threshold condition.</span></p>
	</li>
	<li style="text-align:justify">
	<p><span style="font-size:14px">If |A| &gt; |B|, the relay operates.</span></p>
	</li>
	<li style="text-align:justify">
	<p><span style="font-size:14px">If |A| &lt; |B|, the relay blocks operation.</span></p>
	</li>
</ul>

<p style="margin-left:24px; text-align:justify">&nbsp;</p>

<p style="margin-left:24px; text-align:justify"><span style="font-size:14px">If a phase comparator relay is used,</span></p>

<p style="margin-left:24px; text-align:justify">&nbsp;</p>

<ul>
	<li style="text-align:justify">
	<p><span style="font-size:14px">IF phase angle between A and B is equal to 90<sup>0</sup>, the relay is in threshold condition.</span></p>
	</li>
	<li style="text-align:justify">
	<p><span style="font-size:14px">If phase angle between A and B is less than 90<sup>0</sup>, the relay operates.</span></p>
	</li>
	<li style="text-align:justify">
	<p><span style="font-size:14px">If phase angle between A and B is more than 90<sup>0</sup>, the relay blocks operation.</span></p>
	</li>
</ul>

<p style="text-align:justify">&nbsp;</p>

<p style="text-align:justify"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16251286921625128692.jpg" style="height:1462px; width:800px" /></p>

<p style="text-align:justify">&nbsp;</p>

<p style="text-align:justify">&nbsp;</p>

<p style="text-align:justify"><img alt="" src="https://edupmquestionhelp.s3.ap-south-1.amazonaws.com/hint/uploads/images/16251288671625128867.jpg" style="height:900px; width:800px" /></p>

<p style="text-align:justify">&nbsp;</p>

<p style="text-align:justify"><span style="font-size:14px">The duality between an amplitude comparator and a phase comparator exists. One does not have a phase comparator but only an amplitude comparator is available. Yet it is possible to compare the phase angle between quantities A and B. This is demonstrated in figure 6.23. What all one has to do is add and subtract two quantities A and B vectorially. Irrespective of amplitudes of quantities A and B [in figure 6.23(a), |A| &gt; |B|, in figure 6.23(b), |A| &lt; |B| and in figure 6.23(c), |A| = |B|], if angle between A and B Is less than 90<sup>0</sup>, |A + B| &gt; |A -B| and therefore the amplitude comparator relay operates. Similarly, if angle between A and B is equal to 90<sup>0</sup>, the amplitude comparator relay is in threshold condition. For angle more than 90<sup>0</sup>, the amplitude comparator relay blocks the operation. The same is true for a phase comparator relay acting as an amplitude comparator relay. The demonstration of figure 6.24(a), 6.24(b) and 6.24(c) is self-explanatory.</span></p>