Fewer needed makes for an economical installation
Following the "higher mounting, wider coverage" PIR (Bench Test November 2002), Bosch continues in a high specification trend with the "longer range" corridor-type DS778 PIR. These PIRs result in a more economic installation, since fewer are needed for adequate coverage of larger commercial, retail and industrial premises. The unit has an impressive specified maximum range of 60m, with a width coverage of up to 5.7m and it is housed in a very neat enclosure, the clean lines of which are maintained by the white light filter, which forms part of the cover. Internally, the mirror optics and PCB are attached to single holder frame, which is easily removed for installation. A highly visible, switchable LED is included for walk testing, designed for viewing from a distance of 60m.
Provision has been made for fine adjustment of the mirror in both the vertical and horizontal directions for coverage adjustment. Detector sensitivity can be set for intermediate or high: we carried out our usual performance and stability tests with the high sensitivity setting selected. The alarm output is given by form C (single pole changeover) reed relay. The contacts are rated at 28v DC, 125mA, for resistive loads only. The power requirements are 6-15v DC, 18mA at 12 v.
A first, in our experience, is the provision of terminals for noise voltage measurement, using an external voltmeter. This provides a quantitative assessment of infrared background disturbance. The plastic enclosure consists of a base and a closely fitting cover, held firmly in place by two hooks at the top and a single plastic latch at the bottom. The plastic 'circuit board/ mirror unit' holder is hooked onto four latches in the base. Once hooked in place a single screw through the top right corner of the PCB prevents removal. The single PCB, 69 x 80mm, carries all the electronic components including a rear- facing pyroelectric sensor, terminal connector block, LED on/off and sensitivity selector jumpers, relay and tamper switch. An outer metal shield covers the most sensitive PCB components, but is interrupted by openings for the high output LED, tamper switch and noise voltage test terminals (when used).
The five-faceted mirror slides in curved guides in a plastic sub-frame for a vertical adjustment range of +2 to -16 degrees. The sub-frame slides in curved guides in the 'circuit board/mirror unit' holder for a horizontal adjustment range of +/- 10 degrees.
Scales are marked on left and right edges of the mirror and the holder; also the movement in each direction is notched at one-degree intervals, making progressive adjustment straightforward and secure. The quality of construction is very good and all the component parts are well supported. PCB quality is up to the usual high standard.
Mounting the DS778 should cause no problem but if it does, three different mounting brackets are available as an optional extra: gimbal, low profile and ceiling mount types.
The recommended mounting height is in the range 2 - 2.6m and a table is provided for determining the appropriate vertical angle setting for the required maximum range – 30 or 60m. The vertical angle is adjusted by pushing the mirror up or down in its holder: much easier than the forward or back directions recommended in the Installation Instructions! Weakened sections are provided in the base moulding for fixing screws, brackets and cable entry. A piece of foam is also included for packing around the cable to keep out wildlife! Enclosure integrity is important since the optical system is not separately sealed. When wiring, the alarm loop is connected to the C and NC terminals, bearing in mind that these relay contacts will be open until input power is applied.
It is essential that walk testing be carried out throughout the entire length of the protected area to ensure that not only the vertical mirror angle setting is suitable, but also the horizontal mirror angle. In narrow corridors, it may be necessary to offset the mirror slightly from the centre line, horizontally, in order to obtain full coverage. This is due to the detection pattern coverage, which may be "looking" at the walls rather than the space between them, towards extreme range. The effect is fully explained, with diagrams, in the instructions. A final check, advocated by the manufacturer, is to measure the noise voltage by connecting a DC analogue voltmeter to the noise voltage pins and observing the reading for a period of at least three minutes, with all heating and cooling sources, which would normally be in operation during times of protection, switched on.
Noise voltage readings should not deviate from the base reference level by more than +/- 0.15v DC. The base reference level, measured under quiet conditions, should be approximately 2v; in our test sample it was nearer to 1.75v owing to the loading effect of the analogue voltmeter (50,000 ohms on the 2.5 volt range of our meter).
The pointer of an analogue voltmeter is much easier to follow in this application rather than a digital voltmeter read-out, since the analogue type "averages out" short term spikes.
Access to the noise voltage test pins is achieved by removing a small breakaway section of the PCB screen. A test cord TC 6000 is available as an optional extra: an essential item if reliable contact is to be made with the test pins through the restricted opening in the metal shield. Alignment of the pin polarity markings on the metal shield is useless – refer to installation instructions.
The DS778 was mounted at the usual height of 2m for stability assessment. With the high sensitivity setting selected, it did not respond to the variety of provocations to which it was subjected. The noise voltage readings changed by a maximum of approximately 0.1v with cold air turbulence and 0.25v with hot air turbulence administered. According to the manufacturer, "voltage changes greater than 0.75v DC from the reference level are desirable for good catch performance". The availability of noise voltage externally is a very worthwhile addition. It will turn what is currently a "go/no go" situation to one in which the margin between background IR interference and PIR trigger level can be quantified. We were not able to carry out any tests at maximum range!
What the manufacturer says ...
If you need a long-range intrusion detection solution, but don't want a big, clunky long-range detector, Bosch has the answer – the DS778. Offering a full 200 feet of long-range coverage, the DS778 long-range PIR has you covered.
When the aesthetics of an application are just as important as the intrusion projection, turn to the DS778. Attractively packaged in a sleek, compact enclosure, you get all the benefits of Bosch's award-winning motion detection technology with a look that virtually vanishes in any décor.
The DS778 is the perfect detector to monitor long areas with high visibility where its small design will blend seamlessly into the interior design. Unobtrusive and inconspicuous, the DS778 provides the right kind of security with a great look.
With the DS778, you also get premium performance. Using Bosch's patented Motion Analyser II (MAPII) signal processing, the DS778 intelligently analyses signals to make smart alarm decisions. This detailed process enables the detector to distinguish between different signal sources.
Take advantage of our superior catch performance while reducing costly false alarms and enjoy the savings.
Designed with convenience in mind, the DS778 includes a special high-efficiency light emitting diode. Unlike other detectors, the DS778's LED can be seen throughout the entire coverage area, up to a full 200 feet away. Instantly and easily assess the detector's status from anywhere in the covered area.
The long-range coverage of the DS778 is the ideal security solution for:
- Hallways
- Department stores
- Warehouses
- Large offices
- Schools
With several mounting accessories, you can install the DS778 detector to provide optimum performance while complementing the appearance of your interior. Property owners and installers agree, the DS778 is the ultimate value detector in the security market that provides performance in an extremely attractive design.
Overall assessment
The DS 778 long range PIR intrusion detector has a very impressive maximum detection range of 60m with a width coverage 5.7m at maxi-mum range.With a number of mounting options available, it will no doubt be used for a variety of applications in larger premises.
Outwardly, the DS778 is neat and unobtrusive. Design and constructional quality is very good, both inside and out.
Installation is straightforward, with the circuit board/mirror unit detachable from the mounting base as a single item and the inclusion of a high visibility walk test LED.
The measurement of background IR interference should lead to improved installation reliability.
The DS778 performed very well during stability testing, carried out on the high sensitivity setting.
Sensibly priced, it is good value for money and includes a five-year warranty.
All the written instructions are brief, clear and adequate, accompanied by excellent diagrams.
Source
Security Installer
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