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Wide Beam 40KHZ Ultrasonic Sensors for Air and Gasses

miniature ultrasonic sensor

ultrasonic sensor

HX40TRM Miniature

HX40TRC Aluminium Can

HX40TRE British pipe threads


  • Precision Positioning

  • Wind speed Monitoring

  • Doppler Applications

  • echo Ranging 

  • Level Measurements (Solids and Liquids)

The HX40TR is designed for applications in air. It transmits 120db signal Wide Beam 12 degrees at 40khz. Reception sensitivity level is -51db/V/microbar.  Range from 0m to 20m transceiver to transceiver operation, and echoes from 0.1m to 10m are easily achieved with conventional low cost circuitry. Please note that the crystal settling rate is a limiting factor as to how close an object can be.

The HX40TRE series sensor is protected by a heavy duty chromed brass housing, with 1/8" or 3mm thick walls. This is a 1/2 inch hex junction using BPT standard British pipe thread. Readily available mounting accessories make this sensor easy to apply and install. The sensor can withstand rain, but water film can block the pores of the protective screen, reducing it's sensitivity until the water has evaporated or been wiped off. It should be shielded from rain. 

In the following, two HX40TR transceivers are placed facing each other at a fixed distance. One transceiver referred to as T1 is exited with various voltage levels, and the opposite transceiver referred to as T2 is used to receive the signal. The graphs below plot the output from T2.

plot i plot ii
Above: T1 is exited with a 5Vp-p CMOS square wave oscillating at 40Khz, 100 waves are transmitted. The response as amplitude builds inside the T2 crystal is plotted above.

Above: 5Vpp CMOS/TTL square wave is applied to T1 at various frequencies. The frequency response is measured across the output wires of T2, and plotted above

plot i plot i
Above: Continuous excitation voltage oscillating at 40Khz  is applied to T1. The T2 resulting amplitude is plotted above.

The above illustrates how the output of T2 decays as distance increases between T1 and T2. T1 is exited with oscillating voltage, amplitude 28V.  

plot iii plot iii
Above: T1 was excited with a 30Vp-p 40Khz step input at using signal conditioner HE40SCR, the illustration above shows how long it takes the system to settle on 40Khz. Distance between T1 and T2 is1.5m.

Above: T1 excitation using HE40SCR 30Vp-p FSK (frequency shift keying) signal, low frequency 38647hz (duration 26 waves) and high frequency 40201hz (duration 26 waves). The response was monitored across output pins of T2, placed 1.5m apart from T1, and plotted as shown above. Note that the ripples are digitization errors. 

Cable length between the HE240 series transducers and a signal conditioner, is left to the user's discretion. At 10m lengths the added environmental noise and signal reduction at 40khz is insignificant.

Beam Pattern

The sensor is located in the locus of the polar plot shown below facing north, maximum signal strength is along the 0 degree axis. As the observer with the measuring instruments moves east and west i.e. perpendicular to the 0 line signal strength degrades. The beam pattern character line shown below represents observation angles where signal has degraded by 6 decibels. 

Microchip PIC interface suggestions

The following example, shows how the PIC16C622 and the PIC16C71 can be interfaced to the HE2XX series transducers. For 40Khz transducers C1 an C2 should be about 2nF, R1 about 3Kohms and R2 about 5Kohms. R3 sets the level for the analog comparator of the PIC16C622 and should be high, say 50Kohm. If the A/D converter of the PIC16C71 is being used, R3 should be removed. 

There is an error in the schematic on the right, capacitors marked 2.2pF on the input and output of the operational amplifier, should be marked C1 and C2 respectively. The 4.7k ohm resistor at the input of the opAmp should be marked R1.

schematics

ATMEL AVR interface suggestions

The following example, shows how the AT90S2313 microcontroller can be interfaced to the HE2XX series transducers. For 40Khz transducers C1 an C2 should be about 2nF, R1 about 3Kohms and R2 about 5Kohms. R3 sets the level for the internal analog comparator of the AT90S2313 and should be high, say 50Kohm.

There is an error in the schematic on the right, capacitors marked 2.2pF on the input and output of the operational amplifier, should be marked C1 and C2 respectively. The 4.7k ohm resistor at the input of the opAmp should be marked R1.

schematic

INTEL 8051 interface suggestions

The following example, shows how the INTEL 8051 microcontroller can be interfaced to the HE2XX series transducers. For 40Khz transducers C1 an C2 should be about 2nF, R1 about 3Kohms and R2 about 5Kohms. R3 sets the level for the analog comparator and should be high, say 50Kohm.

There is an error in the schematic on the right, capacitors marked 2.2pF on the input and output of the operational amplifier, should be marked C1 and C2 respectively. The 4.7k ohm resistor at the input of the opAmp should be marked R1.

 

schematic

Electrical Specifications HX40TR

Parameters Values Units
Operating Frequency 39 kHz
Input Voltage 20 (max) Volts (RMS)
Output (SPL) @20V 118 db
Receive (Sensitivity) -56 db/V/Ubar
Impedance 300 ohm
Beam Angle 12 degrees
Bandwidth 2 kHz
Settling Decay 4 mS
Temperature -40 to 100 C
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Copyright 1999 [Hexamite]. All rights reserved. Revised: .

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