+- IRSE Exam Forum (https://irse.signalpost.org)
+-- Forum: MODULES (https://irse.signalpost.org/forumdisplay.php?fid=3)
+--- Forum: Module 3 (https://irse.signalpost.org/forumdisplay.php?fid=6)
+---- Forum: Principles Queries etc (https://irse.signalpost.org/forumdisplay.php?fid=70)
+---- Thread: CCTV Level Crossing Picture Timer relay circuit (/showthread.php?tid=314)
CCTV Level Crossing Picture Timer relay circuit - merlin89 - 07-01-2010
Can somebody explain the function of the attached circuit which forms part of the CCTV Level Crossing Picture Timer relay circuit (IRSE Railway Control Systems page 176). My theory is that when the signaller pushes the picture button which releases the PICTURE.SR the PICTURE Timing Relay will also drop, a 47 second AGASTAT Timer also starts. After 47 seconds has elapsed and provided the PICTURE.SR has picked the PICTURE Timing Relay will also re-energise. Not too sure about how the AGASTAT timer works and I think inductor in series with capacitor with the Picture JR.
Much appreciated
Ian
RE: CCTV Level Crossing Picture Timer relay circuit - eightacre - 08-01-2010
Unfortunately, there does appear to be an error in the circuit depicted on p176 which might explain your difficulties in understanding it. I believe both contacts (PIC SR and LOWER NPR) should be back contacts. See typical circuit X71500.
When the picture is turned on PIC SR drops, providing a feed to the Agastat. The time delay is selected by the value of the resistor, and 470k is usually used in this application which results in approx. 47 seconds. Once the Agastat has timed, the PIC JR will energise, and if nothing else has changed - i.e. barriers still up, PIC SR is re-energised, the picture is blanked and the PIC JR circuit is reset - hence the slow-release feature.
Note that there is no inductor - the book has a slightly ambiguous symbol for a resistor.
RE: CCTV Level Crossing Picture Timer relay circuit - merlin89 - 10-01-2010
Many thanks for the info.
Cheers
Ian