Q&A Dynamic Message Signs Learning Center
In your experience, what should be considered when making a responsible Dynamic Message Signs purchase?
From our experience, it is advisable that the Dynamic Message Signs fulfils:
Visual performance requirements – perfect legibility in any different environmental conditions,
Minimum Operation and Maintenance (O&M) cost during the lifetime of the sign (which is expected to be 10 to 20 years, depending on usage).
In your experience, what parameters should be considered in a purchasing stage, to assure satisfying visual performance?
One should be guided by NEMA or EN12966 standards for visual parameters to unambiguously specify visual performance of the sign. The most important parameters are:
- Luminance (suggested: L3),
- Luminance/Contrast ratio (suggested R3),
- Viewing angle / Beam width (suggested B6),
- Color suggested C2).
Ask for a certificate of conformance to requested visual parameters from the sign vendor. These certificates are widely obtainable in optical labs today.
In your experience, when purchasing a Dynamic Message Signs, what to look for to reduce O&M expenses during sign’s lifetime?
O&M expenses are closely related to the Dynamic Message Signs:
Longevity – the signs are expected to operate with the same level of performance (primarily legibility) over minimum of 10 years,
Reliability – the signs are expected to be operable during all applicable environmental conditions (have least possible failures),
Ease of maintenance – the signs have to be easy to repair, meaning:
a. Repair should be quick
b. Repair should be simple enough for a single technician to repair it
NEMA or EN12966 classification may be used to specify for environmental and structural parameters – they will assure basic longevity and reliability performance.
Besides the NEMA and EN12966 standards, additional proofs of longevity such as test report for simulated 10-year aging of basic sign materials may also be requested.
One may also look for Higher Environmental Protection ratio Certificate (NEMA 6 or IP67).
The buyer can specify the LED Maximum allowed forward current. The vendor may be asked to prove it with signs’ optical certificates.
Detailed explanation of repair procedures may be asked for (description of the procedures, total number of different spare parts, etc.), so the buyer is able to assess differences between vendors.
When specifying the signs, you should use the relevant technical standards to the fullest – from performance classes to the sign dimensions.
Performance classes according to EN 12966 or NEMA: optical, environmental, structural, electrical.
Electric interface: Voltage Supply, Maximum power consumption (defined as: 50% of white pixels are ON under full intensity, including heaters and ventilation on, if needed).
Communication interface: Communication protocol (for example NTCIP standards).
Reliability and durability of LED: LED’s must never be stressed with more than 35% of the rated maximum current (or less). This has to be certified by an independent laboratory and the test reports need to be attached to the offer together with data sheets of the LED’s used.
Reliability and durability of sign materials: proof of longevity, such as test report for simulated 10-year aging of basic sign materials.
- Dimension of graphical part: Display area shall be at least (w × h), full color RGB using at least X × Y pixel to display full color traffic signs.
- Dimension of text part: Display area at least (w × h), full color, amber or white using at least X × Y pixel to display text using proportional letter spacing, text height (as per local standard) for upper case letters; lower case letters and special characters according to local standard have to be provided, letter font X has to be used.
It is standard practice that test reports, proving compliance (class combinations, showing element spacing, brand and type of the LEDs used, and major operating conditions), accompany the offer.
When using relevant technical standards preparing technical specifications, the test method and approval are clearly described, and there is no need for further explanations or definitions.
Vendor knows exactly what needs to be offered, there is no room for misinterpretation or misunderstandings. If the vendor's product doesn't meet the standards, the vendor cannot offer the product.
All offers can be easily compared. All test reports follow the same well-defined, standardized test procedures.
The certificate is confirming that all mandatory tests have been passed, and that specific quality classes have been approved; the tested class combinations are acknowledged in the certificate.
If more than one manufacturer can prove to fulfil the required class combination, there may be still differences in the cost price. The cheapest offer may not the best offer. There may be differences of quality resulting in significant differences in operating and maintenance costs during sign’s life time.
Today users expect sign to have lifetime of minimum 10 years. It means that they have to fulfil all mandatory requirements at least until the end of that period.
Some signs may achieve all quality classes initially (at the time the VMS are installed), but suffer very fast on degradation, clearly visible by decreasing light output.
Based on the test results documented in the test reports given with certificates it is easily possible, to evaluate the quality of the sign.
The key indicator for the power consumption is the LED-current. Test reports, which prove the compliance with optical requirements, have to contain operating current of the LED; if not, the report cannot be used for approval, because any light intensity can be achieved by simply increasing the LED-current, which will reduce the life time of the LED and will increase the degradation of light output dramatically.
Dynamic Message Signs visibility and legibility - from what distance should one be able to see and read the info on the sign? How far on the horizontal axes can you clearly see the written messages (at what distances)?
Legibility is the ability to discern the content of a display, while Visibility is the ability to recognize that a display exists.
The elements that influence legibility of a sign are: contrast ratio of the display, luminance level, the color of the display, the viewing angle of the display, and the uniformity.
Legibility also depends on various environmental and human parameters.
Character height and legibility distance are proportionally related. The larger the character, it will be visible for the farther distance. The factor is typically given in the range 500’ – 600’.
All options are standardly available on all pixel pitches – amber, white, dual color or full color.
Visibility and legibility are assured by NEMA TS-4 / EN12966 optical classes. They assure satisfying legibility and visibility on all weather conditions.
Operating temperature is -40 to +74 °C (-35 to +165°F).
The sign can display:
- Images (graphics) in any standard format (gif, jpg, bmp, …),
- Text in any preloaded True-type font
- Combination of text and graphics, according to NTCIP standard.
- Images are created in any standard image processing tool.
They can be loaded to a sign controller in 2 ways:
- Through NTCIP
- Through Telegra’s configuration software tool
Detailed instructions are available via Telegra support team.
Telegra customizes each solution to the customer. Some of the variables influencing the cost are:
- Pixel pitch (15mm, 18,52mm, 22,23mm, 27,78mm),
- Color option (amber, white, dual color or RGB),
- Access (front or rear),
- Power supply redundancy option,
- Other factors.
Telegra provides do-it-yourself maintenance training for each project. Training is free of charge for the client.
Mounting arrangement will depend on particular project and the support Client is planning to use.
Mounting arrangements are fitted for all kinds of available supports including: Poles, L-shape structures, gantries with or without catwalk, etc.
Telegra products are currently deployed in the following states:
Each sign is delivered with its MIB file that is used by integrator to include the sign into its NTCIP system.
Telegra’s engineers are available for support and assistance during integration process.
In our experience, with traditional signs maintenance assumes direct access to electronic boards and wiring in the sign panel. It is accessed by opening doors at the sign enclosure either from front (doors are segment of front face) or rear. Maintenance technician looks at the internal wiring and electronics of the sign. Technician has to diagnose the error and replace faulty part or wiring. To deal with electronic modules and different kinds of wiring and connectors, technician must be properly trained and sometimes even certified. Technician has to deal with multiple different spare parts. Everything is done on height, in a stressful environment for the technician. During maintenance, doors are opened and internal electronics and wiring are exposed to environmental influences. This can especially be dangerous during humid days when lot of humidity can enter the sign and remain there possibly causing failures due to its conductivity.
Telegra’s NextGen technology is extremely maintenance friendly. The sign is built of modular segments. Each of them is hermetically sealed and resistant to any weather condition. They are interconnected with hermetically sealed cabling. Maintenance technician does not have to open any doors nor examine any internal electronics or wiring. Technician is dealing only with one spare part – the module. Modules are accessed from front or rear side. They can be disconnected and dismounted without any tools, only by hands. Maintenance technician requires much less training than with traditional signs as there is only one spare part involved, process is tool free and technician does not deal with internal wires or electronics.
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