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Surface Patrol

The Model 999J dual temperature sensor measures surface and ambient (air) temperatures digitally. This system senses the pavement temperature under your vehicle as you drive at acceptable highway speeds. The driver is alerted in advance of temperatures that may be approaching the freezing point.

Model 999J consists of three components:

  • A non-contact infrared sensor in an injection molded housing that is mounted under the vehicle and scans the pavement as the vehicle passes over it.
  • An ambient temperature sensor that can be mounted anywhere desired on the vehicle.
  • A dashboard-mounted digital meter that displays the surface temperature as well as ambient (air) temperature to the operator.

QTT Inc. has been producing infrared surface temperature sensors since 1991; longer than any other company. Our customers include Airport Operators, Cities, Counties, Municipalities and state DOT's who are using the units to detect possible icing conditions on runways, taxiways and highways. In doing so, they have experienced more efficient and effective use of sand, salt and de-icing chemicals.

General Description

This motor vehicle mounted, non-contact measurement system continuously monitors the road surface temperature to detect dangerous cold-weather driving conditions. The electronic design of this system provides compensation for the effects of ambient temperature changes which would otherwise result in inaccurate measurements. The digital display output covers a surface temperature range of -40F to +200F (-40C to +90C).

Conditions for Ice Formation

The objective of the QTT system is to continuously monitor road surface temperatures from vehicle moving at normal highway speeds. the provides the operator instantaneous feedback on road surface conditions and an early alert to possible icing conditions.

The higher thermal conductivity of bridges, culverts and other similar surface variations may freeze and subsequently thaw before surrounding road surfaces. When ambient temperatures are near freezing, road surface temperatures can be substantially different, presenting continuously changing driving hazards. The new QTT 999J System alerts the driver that these conditions exist. This dual temperature model also displays the ambient temperature as well as the surface temperature.

Design Characteristics

The 999J Surface Patrol system is a compact instrument designed for easy installation. The sensor head plugs directly into the meter which then provides a digital display of the current temperatures.

Utilizing the latest in electronic and thermal technology, the rugged and compact sensing head converts heat-generated infrared energy into electrical signals which are then translated into calibrated temperature information which is then displayed.


Mechanical installation requires mounting the sensor on the underside of the vehicle. The sensor includes a conical mounting and adjustment assembly to protect the sensor from dirt, water, road debris and vehicle vibration. The meter powers the sensor and requires 12 or 24 volts D.C.

Operation & Maintenance

To operate, simply switch on the vehicle ignition and the system is operational. Maintenance is limited to periodic cleaning of the optical lens within the sensor housing. The frequency of this maintenance is dependent on the operational environment. To clean the lens, unscrew the tube on the bottom of the vehicle-mounted sensor housing and wipe with a tissue dampened with a lens cleaning solution then wipe dry.


Sensor Assembly Injection molded housing with lens protective cone
  Accuracy 0.5F for operating ambient temperatures from 0-120F
  Repeatability 0.1% of full scale
  Shock 50 G's
  Vibration 10 G's in any axis
  Response time 80 milliseconds to 95% of final reading
  RF Hardening Withstands external radio frequency effects caused by mobile radios
  Maximum measurement region 1 inch (2.54cm) O.D.
  Operating Ambient Temperature -40F to +160F (-40C to 70C)
  Supply Voltage 12 or 24 VDC 25%, 150mA max
  Optics Precision Germanium Crystal
  Weight Sensor alone: 2oz (60g)
  w/cables & connectors: 10oz (280g)
Meter Assembly High brightness red LEDs. Displays both Surface & Ambient temperatures in Fahrenheit or Celsius
  Field calibration Adjustable 5F over ice
  Weight 4.5 oz (128 g)
Meter Options Analog or Serial Output
  Analog Output Modes Voltage or Current loop
  Analog Voltage Range 1.00-5.00V, isolated. User programmable gain and offset
  Analog Current Loop 4.00-20.00mA, isolated. User programmable gain and offset.
  Loop power Internal (isolated) or external
  Serial Output EIA/RS-232C, 300-9600bps
  Electrical Connections Compression terminals for input voltage
  Quick disconnect watertight circular system connector
  Data Standards SAE J1708 and J1587
  Cable Length 18 feet (8.5 m) standard

Long-term accuracy not to be affected by harsh winter weather conditions including severe splashing of snow, slush, mud and water.