Intermittently Card Works; Monitored Locks - TDSi EXcel4 User Manual

4.1.8

Intermittently card works

Disconnect the lock and see if the problem still occurs. If this solves the problem then it
may be not the reader at fault but check that the supplied suppression has been fitted
at the lock and also check the lock's power rating. If you are using powerful locks, a
larger lock power supply and/or secondary lock relays may be needed. Thus giving an
intermittent access and appears the reader is only sometimes working.
4.1.9

Monitored Locks

Some maglocks are equipped with "Monitored contacts" which give an output when the
maglock is not powered, or is powered when the door is open. The signal is derived from
the magnetic state of the lock and is supposed to show if a maglock door is closed. The
wires carrying this signal are often within the cable going to the maglock, so it is
convenient to connect it straight to an ACU.
With monitored locks there are three states:
 Circuit closed - When the door is locked
 Door open - when the door opens normally
 Circuit open - When the circuit is broken (This would usually trigger an alarm)
With normal locks, only two states are reported:
 circuit closed
 circuit open
TDSi ACUs are designed to respond only to open and closed states from a lock.
When a monitored contact is connected to the Door Sense contact in a TDSi ACU, then
the door is seen to open as soon as the maglock is powered down and so the lock
power is immediately restored before anyone has had time to enter. Arguably monitored
contacts do not show that a door has actually been opened - anyone presenting a
valid card but then NOT opening the door would be seen as having entered and this
would set any anti-pass back status.
TDSi therefore recommends the use of standard open/close door sensors.
There are two work arounds:
1) Set the ACU to ignore the door sense input ON state for less than 4 seconds.
2) Connect the monitored output to a standard input. This would indicate when
the door was secure, but it would not produce a Door Ajar alarm if something
was preventing the maglock holding the door tightly closed.
The solution to this is to fit a second, conventional door sensor. Then use the
Alarm Shunt feature to disable the monitored contact, and use the
conventional door sensor to break the link between the alarm shunt relay and
the monitored contact. So when a card is swiped, the lock relay is energized,
power is removed from the maglock and the magnetic field starts to collapse. In
the meantime, the alarm shunt relay has also been energized, placing a short
circuit across the monitored contact. So the ACU thinks the door is still closed.
The door opens, activating the secondary door sense input (door open =
contacts open) which disconnects the alarm shunt relay from the monitored
contact. The ACU now thinks the door is open. Both the lock strike and alarm
shunt relays de-energize. Power is now applied to the lock, and as the door
closes, the ACU detects this.
EXcel4 Controller Page 41