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Wide Beam 40KHZ Ultrasonic Sensors for Air and Gasses

 

wide beam ultrasonic transceiver

HX40STRC Aluminium Can

 

HX40STRE British pipe threads


  • Precision Positioning

  • Wind speed Monitoring

  • Doppler Applications

  • Level Measurements (Solids and Liquids)

The HX40STR is designed for applications in air. It transmits 115db signal Wide Beam 12 degrees at 40khz. Reception sensitivity level is -60db/V/microbar.  Range from 0m to 15m transceiver to transceiver operation, and echoes from 0.1m to 7m are easily achieved with conventional low cost circuitry. It must be noted when applying this transducer for echo analysis, that the crystal settling rate is a limiting factor as to how close an object can be. Single conductor shielded cable extends from the back of this sensor, for connection to a signal conditioner.

The HX40S series sensor is protected by a heavy duty chromed brass housing, with 1/8" or 3mm thick walls. It is a standard British pipe thread 3/4 inch BPT. Readily available mounting accessories make this sensor easy to apply and install.

In the following, two HX40STR 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.

 

 

character plot 1 graph 2
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

graph 3 plot 8
Above: Continuous exitation 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 9 plot 7
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 20 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 HX40 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 HX40STR

Parameters Values Units
Operating Frequency 40 kHz
Input Voltage 42 (max) Volts (p-p)
Output (SPL) @20V 112 db
Receive (Sensitivity) -60 db/V/Ubar
Impedance 300 ohm
Beam Angle 12 degrees
Bandwidth 1 kHz
Settling Time 5 mS
Temperature -40 to 100 C
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Copyright 1999 [Hexamite]. All rights reserved. Revised: .

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