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jrautomation.com
Modulated Antenna User Manual - Prelim3
Page 5 of 10
Printed: 11/16/22
3:39 PM
TPM STEM OVERVIEW
The purpose of this section is to provide an overview of the TPM valve stems. The scope of this manual is to
cover the operation of the JR Automation antenna systems that communicate to the stems, not detailed
information on the TPM valve stems themselves. But a general overview of how TPM valve stems operate will
help the users understand the operation of the antenna equipment. It should be noted that JR Automation does
not manufacture or provide TPM valve stems
TPM valve stems are electronic valve stems that are designed to warn a vehicle driver when the tire inflation
pressure is outside acceptable limits. The stems contain pressure sensors and RF communications devices to
allow the stems to detect a bad inflation pressure, and then tell the vehicle computer system that an inflation
problem exists. This allows the vehicle computer to annunciate the problem to the driver of the vehicle, usually
with a dashboard indicator of some kind.
Tire Pressure Monitor sensors or TPM valve stems are manufactured by several different manufacturers. These
stems vary greatly in shape, electrical design, function, communication method, and RF characteristics. It is this
high degree of variation that poses the greatest challenge for a single antenna system to communicate to all
these different stems.
TPM stems are designed to monitor and report on the conditions inside the tire (e.g. tire
internal air temperature, pressure, and stem battery voltage). The stem will transmit this
information via a UHF radio signal (usually 315MHz or 433 MHz). This is typically referred
to as a “wake up”. These wake-up transmissions happen in response to different events,
or in different modes. The one that we are most concerned with utilizes the LF wake up
signal. All TPM stems are designed to respond with a UHF data transmission after
receiving a 125kHz LF wakeup signal. Below is a table of some of the different UHF
wakeup’s that are common to stems.
Event
Common Mode Name
Additional Info.
Inflation Pressure changes
Re-measure or Alert mode
Usually rapidly repeating wakeups
Motion in the wheel
assembly
Drive mode
Can cause wakeups in spinning process
equipment, such as balancers
Time interval
Stationary mode
Stem automatically wakes up at a programmed
time interval, such as every hour
Stem Receives an LF
Radio Signal
Learn mode, LF mode
This is meant for manufacturing purposes and
for use during tire servicing.
This is the
method that JR TPM Antennas utilize to
communicate to the stems.
