FAQ
This list of questions has been compiled from telephone conversation and emails from customers. Note that the questions aren't in any particular order and we will be adding more to the list on a weekly basis!
What is the minimum specification PC I need to use the DL90?
Do Race Technology supply sensors that can be attached to the analogue inputs?
What is a data logger?
A data logger is a system which stores information. In the case of vehicle data loggers,
that information will be measurements taken from car parameters, or parameters relating to
speed and position. Anything from the oil temperature or tyre pressure to steering wheel
position, brake temperature or torque in a driveshaft. Some parameters are easy and cheap
to measure. Others require complicated and expensive sensors. There are literally hundreds of parameters which can be measured. The job of
the data logger is to store these values so they can be viewed later. The three main
factors in choosing a data logger, are:.
Number of channels stored
Sample rate for channels
Storage time (how long you can store data for)
What is the difference
between analogue and digital inputs?
We all tend to hear about digital equipment being the latest
good thing, analogue electronics being the old fashioned, less advanced, technology. But
what does it mean and why is it important for a data logger? Basically, a digital signal
is represented by a 0 or 1, so it’s either there or it isn’t. For a data logger,
this would be something like the brake lights. Either on or off, no half way. An analogue
signal on the other hand is a continuous value. Whereas the digital is 1 or 0. Analogue
can be any number between 0 and 1. On our car, this might be the brake pressure. But what
would be more useful, knowing if the brake light was on, or knowing the brake pressure?
Obviously you get more information from the analogue signal. All data in the loggers is
stored in digital format. Analogue signals must be represented by a series of 0’s and
1’s. The number of bits (binary digits) used determines the resolution of the signal.
If we use 1 bit, we can represent 0 or 1. With two bits we can have 00, 01, 10, or 11. So
we have four levels. 8 bits gives us 256 levels, 12 bits 4096, and 16 bits 65536
levels. So the choice of analogue or digital input depends on the signal being
measured. For analogue inputs, more bits means better resolution. It might seem that the
more bits we have the better. To some extent this is true. But on every signal we are
measuring there will be noise. There is little point measuring a parameter to 16 bit
resolution, when the noise means that only 8 bits is useful. Do you really need 16 bits of
resolution? If for example, this was measuring your steering position, you would have
65536 position steering positions. Is this really more useful than have 8 bit resolution,
which gives 256 possible positions?
Why not have lots of bits anyway, even if it’s not always useful? The chip which
samples the analogue signal and converts it to a digital signal, called an ADC (Analogue
to Digital Converter) costs more the higher the number of bits. To take advantage of the
extra bits, you will also need measurement devices which can achieve the desired
resolution. Finally, if you have two data loggers, one storing the values as 8 bit, and
one as 16 bit. For a given memory size, you get twice the storage time with 8 bit, as
there is only half as much data to store.
What does the sample rate mean?
This is how often the value are sampled and stored. Typically
between 10 and 1000 times per second (10 – 1000Hz) Storing data at 1000Hz will use
100 times the storage space of a 10Hz sample rate. From this point of view, a slower
sample rate would seem ideal. The other side of the coin is that if you sample at a very
slow sample rate, you can miss some detail in the recorded data. What you will miss
depends on what you are measuring. Some parameters change very quickly, such as engine
crank angle, cylinder pressure, or suspension position. Others change relatively slowly,
such as vehicle speed or oil pressure. For the majority of parameters logged at the
clubman level, oil pressure, engine temperature, steering position, acceleration, road
speed, engine speed and so on, 100Hz is more than adequate.
Where is the display for the DL90?
The DL90 is a data logger, it is not intended to provide information to the driver during
a race. It is possible that an external display can be added at a later date to provide
engine speed, vehicle speed, or lap times. Subject to demand and development schedules.
How
is it fitted into the car?
The DL90 is powered from the 12v car battery, this can be either plugged into the cigar
lighter (lead supplied) or directly to the cars electrical system for a more permanent
solution. For a minimum installation, this is all that is required! Optionally there are
inputs for an RPM pickup, wheel speed pickup, digital input, and 2 analogue inputs. All
inputs are on one 8 way connector which can be easily unplugged from the DL90 to enable it
to be easily removed from the car. The serial port for the GPS input is on the back of the
unit, along with the analogue input connector. The serial connector for downloading to a
PC is on the front, so downloads can be achieved without removing the DL90 from the car as
required.
What can the analogue channels be used for?
The 2 external analogue channels can be used for anything which gives an output
between 0-5V or 0-12V. Typically, throttle position from the engine management throttle
pot, oil temperature or pressure from a relevant transducer, brake pressure or anything
else you can get a voltage from.
What can the digital channel be used for?
This can be used for any signal where you only want to know if it’s on or off.
This might be the brake light switch, or could be the output from a lap beacon detector
for lap marking.
What is GPS?
GPS is the Geostationery Positioning System. It is based on a system of many
satellites in orbit which contain very accurate clocks. They transmit a signal to the
Earth, where a small radio receiver can listen for upto 12 satellites at the same time. By
knowing where each satellite is, and knowing how long it took for the radio signal to
arrive at the receiver, it can calculate the distance to each satellite, and therefore the
position of the receiver. Not only can it measure the position, but by measuring the
position every second, it can calculate the speed at which you are traveling.
How accurate
is GPS?
The absolute positional accuracy for a standard, commercial, GPS system is around 2m
to 3m with ideal conditions degrading to about 15m with poor conditions, but if you want
to spend $10 000's you can get it down to a few cm. Whilst the standard GPS system
doesn’t sound great, this is the absolute positional accuracy. The accuracy from one
point to the next, which is used for speed measurement, it much better than this. What
this means is that although you might not know your exact absolute position, you can get a
very good speed measurement. The software also combines the output from the accelerometers
with the GPS data to further enhance the accuracy.
If GPS is so good, why do
you bother with accelerometers?
Although the speed data from the GPS is very
good. It is only updated once per second, and is not available at all if you are driving
under cover. Accelerometer measurements are taken every 10mS, so the information is much
more detailed. Combining both acceleration and GPS data allows for greatly increased
accuracy than using either one in isolation.
What is the minimum installation for the DL90?
The minimum installation is power from the car and the GPS receiver mounted with a
good view of the sky.
How does the DL90 download the data to a PC?
Using a standard RS-232 serial port. Data download rate is approximately 18 x storage
rate. So a 15 minute track session will take around 50s to download.
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How do you calculate lap
times without a optical beacon?
Because the DL90 uses GPS as one of it's key inputs, it can calculate the exact time when the vehicle passes any given point. To calculate a lap time you define a start/finish line somewhere on the track, the software then calculates the times when the vehicle crosses over the start/finish line and can calculate the time in between each crossing to give a time to complete a lap.
Sector times are calculated in exactly the same way as lap times, in fact the software doesn't even differentiate between them. Up to 1000 track markers can be added to a track making a huge number of sector times possible!
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Does the software use metric or imperial units?
The preferred units for the DL90 are standard SI. However in nearly all cases the
relevant imperial units are also accessible.
How do I get support for the DL90?
At Race Technology we pride ourselves on the quality of support, if you have any
questions then please go to the DL90 support
page.
What is the minimum specification PC I need to use the DL90?
We have spend a great deal of effort making our software work on relatively modest
PCs. As well as optimising processing and searching algorithms, we even went to the length
of writing our own graphing routines to improve the performance. We have tested the
analysis software on a 233Mhz PC running windows 98 and it was absolutely fine. One thing
to bear in mind however is the memory requirements for a long run. The memory requirements
can be calculated quite simply:
memory required = the number of samples x number of variables required x 4 bytes
(approximately)
So for a 20 minute race with a (typical) 10
variables required you will need at least 5 MB memory, in the worst case, a 89 minute run
with 25 variables you would need at least 52MB of free memory.
By far the most computationally complex task of the analysis software is the initial
processing of the data. On the 233Mhz PC this took about 1 minute 30 seconds for a 20
minute 10 lap race. However, once it is processed, all the graphing and analysis was fast
and very useable. The software works fine at all resolutions supported by windows.
However, as so much data can be plotted on graphs, the higher the resolution and
the bigger the screen the better. A resolution of 800x600 should be considered an absolute
minimum and 1024x768 or higher is recommended.
What operating systems does the software work with?
The software has been tested with 95, 98, ME, NT, 2000, and XP. In all cases you will
need the latest service releases from Microsoft to ensure trouble free use. For further
details of what service packs are required see our support page. The software development
was carried out on windows 2000, so this is the preferred OS. We haven't got any plans to
support MAC OS at present.
Is the
logger upgradeable?
Absolutely yes. Not only will we be offering free upgrades to the PC analysis
software, we will be offering free firmware upgrades for the DL90 itself to upgrade the
units performance or add new features. Incidentally if you have any suggestions of what
you would like to see added to the meter let
us know!
Can the DL90 be permanently installed in the vehicle?
Yes, no problem. The only limitation is you will obviously need to access the serial
port (although you could attach an extension cable) and it is often useful to check the
status LEDs on the unit.
Do Race Technology supply sensors that can be attached to the
analogue inputs?
Not yet, but we are actively trying to source sensors of sufficient quality at a
reasonable price. If you are after anything in particular, please let us know so we can
advise you.
Can the DL90 be used on trackdays?
Most trackday companies will not allow timing devices for insurance purposes. As
the DL90 does not give any timing information when on the track, it is not classed as
such. Easytrack in the UK are happy for
people to use the DL90 on any of their trackdays.