EXAMPLE: We added two new access control doors to an existing four-door system which had been in service for about five years. Originally the system designer did the calculations and specified the correct wire. During the upgrade the installers did actual voltage measurements during system deployment, but still a problem was reported the day after the new doors were turned over the doors to the customer.
It turned out that the power supply backup battery was worn out and was consuming power rather than reinforcing it. The voltage at the furthest door was dipping down to the marginal level and our equipment was operating erratically. A new battery resolved it.
During troubleshooting, this battery was reading low even while connected to the trickle charge and it would not have powered the system in the event of an interruption of, or dip in line voltage to the system power supply.
Access control cabling could include voltage outputs to electric locking devices and fire alarm interfaces. Shorts, opens or weak connections on these cables of course can result in problems.
When setting up systems, I always include a slave relay. They provide electrical isolation between the control and on board output contacts and the electric locking device. The relay’s contacts actually switch the voltage to the lock, protecting the controller from possible noise kickback, and also from the damage to the contacts repeatedly energizing the electric lock. Should there be a problem with the lock or a short somewhere in the control circuit, the relay contacts will take the hit rather than components on the controller. It is cheaper and easier to replace a relay than a controller.
The relay coil is what the controller has to energize. Relay coils are low current, usually under 50 mA. Electric locks and maglocks draw more current and are typically inductive loads throwing spikes and surges back across the controller’s contacts if the lock is direct wired to them. Varisters and diodes are used to suppress the noise, but it is better to isolate your circuits and use suppressors as well.
Relays cost around $10. Diodes and varisters are often provided with locks and controllers or can be purchased inexpensively.
Switching/Signaling Cabling might include things like Request to Exit switches and door position sensors. Door position sensors usually do not carry current. Request to Exit sensors and pushbuttons may or may not switch the lock power.
Where maglocks are used, it has been recommended practice or mandated by code to provide redundant life safety to door systems by using the REX as an additional means to cut power to maglocks so emergency egress can be assured even if other system elements fail to operate. So if a maglock is not operating properly, the REX may be the culprit and needs to be tested as part of the troubleshooting process.
Voltage (AC & DC) is the amount of charge between the sides of the circuit, the electrical force, or “pressure”, that pushes current through wires. It is measured in VOLTS (V or E).
Current (Amps) is the movement of electrical charge (electrons) in a circuit, similar to water through a hose. The rate at which electrons flow through a circuit is measured in AMPERES (AMPS, A or I)
Resistance (Ohms): is the limiting of electrons that pass through a circuit, adding resistors or changing wire size limits the rate of electrons moving through the circuit. Measured in OHMS ( ? or R ).
Power is measured in Watts. May also be represented by (P). P = I x E
Troubleshooting Tools: Multimeters, Toner/Tracers
Multi-Meters are probably the technician’s most versatile troubleshooting tool, used to measure voltage, resistance and current.
There is an endless debate over which meter is best and how much it is necessary to pay in order to buy a good meter. For me a meter has to be Accurate, rugged enough to withstand falls and abuse, convenient to operate with an easy to read display and operate control face, and be adequately insulated to protect me from electric shock. My Fluke 112 is not the top of the line, or the latest model, but it serves me well, and has for at least a decade. Multimeters are used to measure voltage, resistance and current.
Toner/Tracers can be life savers in a variety of scenarios. A toner/tracer such as the Fluke TC90 is a multi-function tool capable of three functions:
Occasionally when installing access controls, things will not go the way you thought they ought to. Some call it a “bug” or a “ghost in the machine,” but your equipment is misbehaving. There...