Signalling change

Some of the greatest changes in our industry over the last few years have been in the signalling systems that we use. The reasons for this change include the requirements of the ACPO Policy together with an increase in the use of Type A systems and advances in communications.

Also significant is the Clean Neighbourhoods and Environmental Act which aims to reduce the pollution of noise from intruder alarms.

The introduction of the EN Standards itself brought along new issues on signalling for the different grades and the high standards and widespread use of mobile communications is now taking us into new spheres.

The 'Level 3 Certificate of Knowledge of Security and Emergency Alarm Systems (1852)' syllabus covers our industry and includes the intruder alarms signalling objectives in Section 06 of the 1852-001 System Technologies.

Students on the course are asking for increased information to be made available in our training plans to cater for developments in remote signalling and the effect these are having on installation practices. A lot of questions have revolved around the connection of the telephone line and dual path signalling.

Signalling types

In broad terms, for the intruder sector we employ audible, visual and remote signalling. Audible is by sounders, visual is by strobes or beacons and remote is by communication devices. Video images may also be used in integrated systems.

Although audible techniques have formed the backbone of alarms for a long time, the days of using high output sounders must surely now decline. The European Norms include communication devices as an option in every grade but with different requirements laid down to reflect the maximum time and attempts that it takes to communicate remotely.

As we move up through the grades, measures must be taken against equipment substitution including the use of encryption and methods of protecting the data transmitted.

This means that many established speech diallers cannot be graded because there is no periodic testing of the line to the ARC although these devices still have a huge part to play in a supporting role. The domestic low risk speech dialler is simply plugged into a standard telephone socket (BT601A) using a lead with a BT plug. This is uncomplicated because the line box or master socket NTE5A (Network terminating equipment) provides a clear demarcation between the telephone operators network and any customer extension wiring.

This line box also holds an insulation displacement connector (IDC). This is the familiar insertion connection socket so additional telephone points can easily be added or relocated by the customer with the BT line disconnected.

If we think of true monitored communications however, BT redcare comes to mind. It comes in a variety of different packages, all of which involve specific industry connections to the telephone line. This is in addition to the terminations we must make for our general security cabling.

The essential redcare system uses an existing PSTN (public switched telephone network) line to provide a secure connection between a subscriber's terminal unit (STU) and an Alarm Receiving Centre. It has two-way monitoring, so is able to detect a line cut, and it has encryption to prevent the substitution of equipment.

The STU is a communication component of great interest to the security installer. It features both telecommunication network voltage (TNV) and safety extra low voltage (SELV) circuits so there are distinct connections to make. Remember that direct connection or interconnection via other apparatus to the line can produce hazardous voltages on the telephone network. However an external plug in connection to the telephone line cannot be made as this would be insecure. Therefore precautions must be made.

In order to comply with safety regulations:

• TNV terminals should only be connected to PSTN or other circuits designated as TNV circuits.
• SELV terminals must only be connected to other circuits designated as SELV circuits.

Connection of the telephone line

The connections to the STU redcare terminal block provided by BT must be made before connecting to the PSTN. A single strand earth 1mm minimum must be made and taken to a good earth point. Solid core CW1308 1/0.5mm cable should be used to connect the telephone point terminals. These are identified on IDC blocks as follows:

A or (5) colour identity WHITE/blue

B or (2) colour identity BLUE/white

On some BT redcare terminal blocks a telephone set C terminal can exist, but the terminals may not be identified. If so the A, B and C points can be determined as follows:

Use a multi-meter on 50V range and identify the B terminal (common) 50V to A and

I certainly see a much greater use of remote signalling packages for the future including SMS messages to mobile phones…

50 V to C. Using the 500mA range measure the current between both A to B, and B to C, the highest reading is A to B 100mA approx. and the lowest reading is B to C 40mA approx.

It is worth remembering that C on an IDC point is terminal 3 and it uses the colour identity ORANGE/white.

Of course a huge variety of communication equipment is now available to satisfy the industry needs. As we are aware, the digital communicator is used to transmit alarm signals including sequential confirmation of confirmed activations to an ARC or monitoring station using a number of different formats.

Taking this a stage further, a digital communicator with a modem can connect to a PC based at a remote engineering centre equipped with specific software to upload or download the system parameters (including the event log and diagnostics).

It can also set and unset the alarm system and carry out additional special functions, print logs, observe events and even change user codes. Digital communicators are intended to be connected directly to an ex-directory line used exclusively for alarm communications.

If an exclusive line is unavailable and other apparatus such as an answer phone is connected to the line, the communicator should provide a series connection with line divert for the other apparatus.

When triggered, the communicator is designed to seize the line and to disconnect the other apparatus while it remains operational.

When the communicator has completed its operation it will then reconnect the other apparatus.

In other respects the connection of the line is similar to that of the STU although some end stations do have an internal RJ11 plug in connector to make the connection simpler.

For divert, the A and B lines must be connected correctly for polarity as Figure 1on previous page.

Dual path signalling

Otherwise called dual communications, this technique features a duplicated transmission medium in that it uses two technologies – landline and cellular radio network.

It is a secure service that can transmit a confirmed alarm if the landline or cellular paths are attacked regardless of the first to be affected.

It is used for Grade 4 high risk sites as it is capable of protecting a customer's Level 1 police response. It would tend to be to Environmental Class 1.

There are a number of different types of dual path systems but they are all essentially combined land line and wireless reporting devices.

Figure 2 shows a typical STU that is used to carry out dual path signalling using the BT redcare system. Therefore it should be noted that this STU includes both a GSM (global system for mobile communications) transceiver with a SIM card carriage plus the PSTN line connector block.

Increased radio signalling

Using such a dual signalling technique means that the radio signal can be brought into effect in the event that the normal hard wired line is cut, if the panel fails or if any disruption occurs between the intruder alarm control equipment and the monitoring point. The increase in reliability and the rapid advances that have taken place in the cellular networks have lead to a far greater use of radio signalling within all communication systems including its use as a support technology.

Do not forget that the same restrictions apply to a radio reporting device as those of a mobile telephone. A consideration is that if the signal strength is weak a better position must be found for any communication devices incorporating cellular equipment. Higher gain extension antennas and extension cables are available for this purpose. Always check the specific manufacturers' data for connection details. For instance, the GSM/STU must use a BT block terminal 92A with the incoming line made to the IDC portion and the STU connected to the clearly identified A and B lines with screw terminals.

Of course, communication devices are designed with industry standard footprints so can be used as standalone or plug in units. However there is still a need for the security installer to become familiar with the range of allocated PCB pins and channels together with the programmable inputs/ outputs and defaults. With digital services which include BT redcare, more information can be transmitted, intruders can be tracked and there may be integration with systems such as CCTV. I can certainly see a much greater use of remote signalling packages for the future including SMS messages to mobile phones plus greater inroads being made by video images and audio listen-in modules. Remote signalling/communications have got to be the future of security signalling in a respected industry. However do not forget the practical elements and the need to consider any extra power supplies, the addition of the extra Ringer Equivalence Number (REN) for the communication device and any causes that might prevent transmission.

Always study the manufacturers' data carefully and never overlook the industry methods needed to counter incoming calls, easy disconnection of the line and the importance of using only with compatible PABX (private automatic branch exchange) switchboards.