LET'S TALK ABOUT PULSES - Fred Stock - www.TaxiCabElectronics.com
Your taxi meter needs to know how far it's car has traveled in order to calculate the fares you will charge. . . . First...
If you were to glue an unlimited number of yard sticks to the curb, and as you drove up the street and passed each stick,
some sort of signal were generated in your car. you could count the pulses on the block. Now, think about that. The faster
you drove, the faster these signal pulses would come in, and the further you were to go, the more of those pulses you would
be able to count. If you know how many pulses there are on one block, you could count the pulses and know if you had
gone half the block, twice the block.. whatever.
There is a device in most cars which makes pulses which are generated in the same way. The further you go, the more the
pulses accumulate. These are always a true representation of the distance your car has moved. When you stop, the pulses
stop, when you move on, they resume. It has worked that way for over two decades and we have been able to count on them.
Some cars have several places which can generate acceptable pulses. ... Except ...
Some very old cars (before maybe 1985 or 1990) had no such electronic circuit and operated their speedometer and odometer by mechanical cables. In order to add electronic taximeters to such vehicles, we must add a device called a "transducer" to the mechanical cable. The transducer is then rotated with the speedometer cable whe it rotates inside. The transducer has magnets and a coil inside, and as it turns, the device creates a series of electrical pulses. These are also an accurate representation of the distance traveled. The whole system worked well, but transducers, being by nature, mechanical devices, were prone to wear, mechanical damage and electrical deterioration. It works, but it is more fragile than we would want.
Some of the very newest vehicles (perhaps 2011 to 2012) have no usable pulse in their systems. The auto industry has evolved into the computer age, dropping a pulse-series for computer data flows or some other system which will not satisfy our meter requirements. In these few cases, we have a device which can be plugged into the "OBDII" diagnostic plug in your car. This device extracts the necessary computer data, and generates a pulse which the meter will like. It plugs into the OBDII jack - usually under the dashboard near your knees - and has one additional wire which is easily connected to key switched power. The output is connected directly to your meter pulse input lead.
Regardless of how the pulse train is created, it is fed to the little computer in your meter. There is a function among the
programming sections of all meters, which allows the meter to be used as a pulse counter by the installer. We install the meter, then
drive our vehicle over a perfect 5280 ft. - one mile course, and let the meter count the pulses. At the end of one exact mile, we punch
the appropriatebutton, and lock in the number of pulses it counted. Suppose there were 8402 pulses. Now since the meter knows there
are 8402 pulses in a mile, if is sees 16804 pulses during a fare, it knows it has gone two miles, or if it sees 4201, it's moved one
half mile. The process of counting and storing the accurate count in one exact mile, is called "calibration".
Since it is a calculator, the meter computer can now take the program it has in it, and figure out the fare, and keep track of statistics
such as distance you drove, money you earned, number of trips you have made, etc..
When we program a taximeter, we tell it what the Flag Drop fee will be and what the initial distance will be. (The term "flag drop"
came from the old time mechanical meters which had a 'flag' like a mail box flag. To start the meter, you pulled the flag handle down.
That started the meter, and gave the client a certain travel distance for that fee. The flags are gone but the name is still there.) After that
initial distance is reached, the meter shifts to Mileage Fee calculations. We have specified the fraction of a mile we will use and how
much we will charge each portion so our fare comes out to the proper fee per mile. For instrance, suppose we want to charge $2.00
per mile. We could charge 25-cents every eighth of a mile. We could also charge 20-cents every tenth of a mile. We could even
charge 50-cents every quarter of a mile. I suppose there might be other sets of numbers that might work as well. However we set up
the schedule, the computer takes the pulse count, figures out the rate numbers, and displays the fare up on the screen. When you buy
or install a taximeter, you must specify the rates you will charge. They are programmed into the meter's computer, and with the pulse
count, the device has all the data it needs to properly compute fares. Notice, if the meter is not properly calibrated to the mile, it cannot
correctly figure the fare. It may be high or low, but not accurate.
Some vehicles like very late model Chrysler vans (Dodge, Plymouth, Chrysler etc. and others) have an extremely high pulse count. They are sometimes so high in pulses-per-mile that they exceed the acceptable range of your meter. We handle a number of devices called "pulse dividers" which can divide the pulse count by 2, by 4, 8, 16, even 32. It simply takes the pulse from the car, processes it through a tiny computer, and sends the reduced number of pulses to the meter. You calibrate the meter after the correction is made, and you're in business!
Things that commonly cause pulse losses in your car include broken wires between the pulse source and the meter, loss of power to
the pulse divider unit, wires which were run through a metal barrier like your firewall, and have chafed causing them to be grounded.
This shunts the pulse signal to ground, and effectively kills the pulses. You will become aware of a loss of pulses quickly, since the fare
suddenly falls to one half or one third the normal rate. When it hits your profit, you notice! Eh?
Your meter is capable of generating dollars for you in three ways; distance you travel, time you wait, or extra fees you inject with the
"Extras" button. Assuming the extras button has not been used, and your have been getting normal fares just as you expected,, suddenly your fare is a fraction of what you should be getting. The pulses have died for whatever reason, and the meter is now running only on time. If the pulses are not there, the meter has to assume you have stopped and are waiting for someone. Thus,waiting time charges only. Ouch! Test by simply turning "TIME OFF" and drive, If there is no fare coming up, no pulses!
The pulse source in each vehicle is unique to that vehicle. No two vehicle types are exactly the same, and an installer may have spent
years gathering the information he needs to properly install your taxi. We have created a program of installation instructions which have
exact color codes of wires, locations of power and pulse sources in a particular make model and year of vehicle. They also carry complete
programming instructions which you would need if you wanted to change rates later. (We pre-program your meter if you buy it from us.)
The instruction packages also include complete calibration instructions you will need after you have the meter installed. To get the exact
package you need, look at the home page of www.TaxiCabElectronics.com, and click on "INSTALLATION INSTRUCTIONS" in
the middle of the product and services chart. We'll need to know your exact year, make and model of car, and which meter you are
going to install. Also give us your telephone number in case we have questions to allow us to get it right the first time.
Oh, one note for our Canadian clients and friends elsewhere who measure in kilometers: Since the meter calculations are based on
the number of pulses you tell the meter to use as a standard, lets say 8000 for sake of discussion, the meter DOES NOT KNOW
whether you are specifying a mile or a kilometer. It only knows you have said "this number is our standard." If you use miles and travel
one mile whilst calibrating, and lock in 8000, or if you travel one kilometer and lock in 8000 pulses, regardless, the meter only knows
8000. So if it sees 4000 it knows it has traveled half the distance - whatever that is. If you used km and full fare for 1 km is $2.00, it will
register $1.00 on 4000 pulses. It doesn't care what unit you are using. Does that make it clearer? Whatever standard you use - Martian
Gazortmas will work - meters register according to pulse count. (So far, we have had very few clients using gazortmas, but you never know
in this business!! ;-)
If you are interested, the distance calcs are these: One Kilometer = .62137119224 Miles. One Mile = 1.609344 Kilometers. If you want
to convert one to the other, simply multiply: Multiply your Kilometer distance by .62137119224 to get the same distance in Miles. Multiply
your Mile distance by 1.609344 to arrive at Kilometers. That's accurate enough to get it down to tenths of an inch (0.254 cm!!)
But remember, your meter does not need to know anything except the number of pulses you are using as a standard. YOU of course, and
your inspecting officer will know which applies in your area, and your meter will output the correct fare if you use THAT system for your
count during caalibration. (We are waiting for the gazortma conversion chart, but apparently it has to be sent a very long way! :-) )
We trust this helps you understand the pulse system which gives your meter the data on distance it requires. - Fred Stock 3/11