The 4 most important rules for selecting onsite environmental logging hardware

Are Tablet PCs the answer?

Rugged Tablet PCs have improved a great deal in the last 3 years and are now a viable competitor to PDA devices for many logging applications.

Tablet PCs have a couple of major benefits over PDAs and this article highlights the four most important rules you need to abide by before deciding whether to use PDAs or Tablet PCs to log environmental data onsite.

1 – Screen Brightness
If you take a standard laptop outdoors in bright sunlight then the chances are you won’t be able to see much detail on the screen without twisting the device to get as little sunlight interference as possible. This problem makes standard screen devices, such as laptops and mobile phones, impractical for use in an outdoor environment.

Let me introduce you to a NIT. A NIT is a luminance unit equal to 1 candle per square metre measured perpendicular to the rays from the source – see you’ve learnt something new already!

This scientific explanation does not make a great deal of sense to a layman but it is extremely useful when comparing devices. To give you a base line to start from, the standard laptop and desktop screen operate at around 200-250 NITs. Standard Rugged tablets for use in industrial settings and warehouses currently come with a 350 NIT screen as standard.

Increasing the NIT rating of the device by increasing the backlight in the device requires more power and therefore decreases the battery life of the device – just like a really bright torch seems to eat up batteries quickly!
Outdoor Rugged screen are now available at up to 1200 NITs. These devices can actually be painful to read indoors because they are so bright, but they are excellent for outdoor use.

Rule 1 – Never buy a device unless you have tried to use it on a bright sunny day.

2 – Battery Life
One of the biggest concerns with using electronic devices to log data is what happens when the battery dies. There are two problems when this happens. Firstly, was any data lost when the machine powered down? Secondly, what options are available for powering the device up again?

Data loss concerns have been well addressed by the industry with the use of solid state drives and hibernating routines for the operating systems. However, just like laptops, if a tablet PC runs out of power half way through shutdown this can cause restart problems.

The main concern that needs to be reviewed when selecting hardware for outdoor logging is how long the device will work for without needing a recharge? PDAs generally use a lot less power than their tablet counterparts and it is common to find rugged devices that come with a 5 – 6 hour up time on a single charge. This, coupled with an instant boot up time, allows the machine to be easily turned off when not being used, easily extending the battery life to a full working day.

Tablet PCs are more power hungry and therefore need large batteries. If you should find a device that claims to work for a day on a single charge look out for the weight and cost. Many tablets now come with hot swappable batteries that allow you to change the battery without powering down the device and this can work well if you are close to a recharging source.

Rule 2 – If a full day’s use is important and you do not have access to recharging facilities then be very sceptical when considering Tablet PCs

3 – Ruggedness

IP or “Ingress Protection” is an internationally recognised classification system (EN60529), demonstrating how well sealed enclosures of electrical equipment are against foreign bodies. In layman’s terms it’s a measure of how dust and water proof a device is. IP ratings always come with 2 numbers, “IP54” for example.

The meanings of these two digits are explained further in the table below:

First Digit:

Protection for the equipment against ingress of solid foreign objects

Second Digit:
Protection against ingress of water with harmful effects
0 (non-protected) (non-protected)
1 ≥50 mm in diameter back of hand
2 ≥12.5 mm in diameter finger
3 ≥2.5 mm in diameter tool
4 ≥1.0 mm in diameter wire
5 dust-protected wire
6 dust-tight wire
X not required
0  (non-protected)
1  vertically dripping
2  dripping (15° tilted)
3  spraying
4  splashing
5  jetting
6  powerful jetting
7  temporary immersion
8  continuous immersion
X  not required

Most tablet devices range between an IP rating of IP54 and IP67. In almost all cases we have found that the difference between these two levels of protection adds around £800 to the cost of a Tablet and around £400 to a PDA.
It is important to realise that the 2 code IP rating does not include impact protection as thisis a common misconception. Although there are standards for impact protection they are rarely quoted. Instead physical tests are described like the ones below.

• Shock: 30 g for 11 ms (non-rotating disk)
• Drop test: 4 feet on concrete, 26 directions (drop)
• (Flash disk in operating and rotating drive in nonoperating mode)

The final thing to consider is how likely the screen is to be broken by impact. If you drop a device so that a sharp object hits the screen first the likelihood is that it will break. PDAs can do a lot more to protect their screen especially if the screen is well recessed but Tablet PCs have a much harder job.

Rule 3 – Always ensure the device’s IP rating is high enough for your requirements and that you are aware of the drop rating of the device.

If you are going to carry a device with you all day then small and light are two features you will want to look at as well as the above. Some Tablet PC’s weight 2KG and require both hands to use while PDAs weight around 600g and can easily be strapped to your wrist.
At a recent conference two people independently said that they would choose a PDA over a tablet as it will fit in bucket and be carried with the other items!

Rule 4 – Be aware that even when you have considered all the technical aspects you must remember that there are the practical elements to consider.

There is no point having real time onsite logging equipment if it is left back at base …..

I’d be very interested to hear if you have additional rules or experiences with onsite logging. Please use the comment box below if you agree, disagree or have something to add to the above.

Roger Chandler

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