[K3CAL] Tire Pressure Sensor

Mon Nov 17 20:58:27 EST 2014

Hi Shawn 

A recent article about TPMS stated that since TPMS has been required by law (as of the 2008 model year) vehicle related deaths due to tire failure have decreased. 

Attached is a photo of 3 different styles of sensors. They are encapsulated with 
some sort of potting material that makes it impossible to service the battery. I imagine 
the purpose is to protect the electronics from the environment 
of the inside of the tire/wheel assembly. Being spun around hundreds of times at 60 mph is 
probably very harsh on un protected electronics. 

Depending on the system style your car knows to listen for only your tpms sensors. The on board computers are programmed to listen for a specific ID number that is transmitted by the sensors installed on your car. Think of it like the 'CTCSS tone' needed to key up a repeater. The signal from the sensor is a very low digital RF wattage. This ID number of the sensor is programmed into the cars computer from the factory and at any time a new sensor is installed.

 On systems that are able to tell the driver what wheel position is low on air the ID's listed in the computer are linked or associated with a wheel position 

ID# A =  Right Front 
ID# B = Left Front 
ID# C = Right Rear 
ID# D = Left Rear 

On some systems, when tires are rotated it is important to update the ID's with the current wheel position association. This ensures that the systen will properly ID the correct wheel position 

ID# C = Right Front 
ID# D = Left Front 
ID# A = Right Rear 
ID # B = Left Rear 

Some systems are smart enough to sort out ID's and wheel positions all by them selves, other systems don't care about wheel position at all and only light a warning lamp indicating a possible low tire somewhere on the car.

With the multiple styles and types of systems on the road it is important to have the correct equipment to service the tpms systems properly. We find many problems with TPMS are caused by improper service from discount stores. Perhaps they do not or can not spend the money on the tools and the training ?

A cool benefit of having the right equipment, is I can read tire pressure with out ever touching the car. A handheld device, (much like a bar code reader) is used to trigger the sensor and retrieve the data that it transmits. 

Tire Pressure Monitoring Systems are just one of the neat pieces of technology found on today's cars that are somewhat ham radio related. Basically TPMS is simply a digital packet transmitted in the 70cm band at a low RF output level. 

Probably more than you want to know,...
 But I am a ham, I have a federal government issued permit to talk. Well in this case.. type.  

Brian
KB3WFV    

--------------------------------------
On Mon, 11/17/14, N3AE <n3ae at comcast.net> wrote:

 Subject: Re: [K3CAL] Tire Pressure Sensor
 To: "Kress, Brian" <kb3wfv at yahoo.com>, "Reflector, K3CAL" <k3cal at mailman.qth.net>
 Date: Monday, November 17, 2014, 4:23 PM

 Thanks
 Brian,

 Interesting stuff.   I thought
 TPMS was a "feature" and didn't realize it was
 mandated by law.

 Have you ever taken apart a sensor
 to see what type of battery it uses and how the battery is
 attached to the circuitry?   I'm guessing that battery
 replacement isn't possible because almost any way of
 making a detachable battery connection in the harsh
 environment of the wheel would not be very reliable.

 Wonder
 how my car knows to read only it's own tire sensors and
 not react to sensors on another car that pulls up next to
 mine at a stoplight?

 Shawn
 From:
 "Reflector, K3CAL"
 <k3cal at mailman.qth.net>
 To:
 "Reflector, K3CAL"
 <k3cal at mailman.qth.net>
 Sent:
 Monday, November 17, 2014 2:25:33 PM
 Subject: [K3CAL] Tire Pressure Sensor

 This morning on the
 985 mach I had a conversation with several of you about 
 tire pressure sensors found on all cars model
 year 2008 and newer.

 Tire pressure sensor are a wireless
 sensor mounted on the base of the tire valve stem inside the
 wheel..
 They transmit on 315 mhz and 430
 mhz

 Here is a
 link to our web site with a couple of videos about Tire
 Pressure Monitoring Systems (TPMS)

 http://marlborotire.com/tpms-tire-pressure-monitoring-systems

 Brian
 KB3WFV
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