Reference Target Temperature Compensation (RTTC) is an advanced temperature compensation for our ultrasonic sensors. Ultrasonic sensors measure the time to receive echoes from distant surfaces. When air temperature changes so does the speed of sound, so a stationary surface appears closer or farther away when echoes are quicker or take longer to arrive. Our sensors have built-in temperature compensation. Compensation done internally can result in under- or over-compensation during times of rapid air temperature change such as at sunup or when the sensor is warmed midday. RTTC overcomes that by measuring two targets each cycle. A closer reference target is used to adjust the measurement of the farther user’s target, in real time. For example, a stream measured with internal temp compensation and with RTTC are illustrated below for a 48-hour period.


RTTC requires a reference target which is placed in the sensor field of view and is unmoving. Accessory targets are available from Senix for our ToughSonic sensors with 30mm or 1” NPT threads. These targets can be used in the open, or the sensor can be mounted into a 2” NPT threaded riser, flange, stilling tube, or tank bung. RTTC works on Serial-only or Serial plus analog and switch output sensors. Targets for other ToughSonic models will be added. RTTC is applicable to all Senix sensors. A guideline to making your own reference target is available through Senix customer support.

Do not use Reference Target Temperature Compensation without a reference target installed, or the sensor will not perform correctly.


RTTC calibration can be done at any time in any temperature from within SenixVIEW. A step-by-step calibration is given below.


To install and prepare Reference Target Temperature Compensation for use


  1. Install SenixVIEW version 3.6.200 or higher to your PC, available at www.
  2. In SenixVIEW, upgrade the sensor firmware to version V47.fwu or higher.
  3. Install a Reference Target (RT) with thread adapter accessory to your 30mm or 1” NPT sensor. The target surface is the bent area at the tip. Do not alter the accessory by bending.
  4. Mount the sensor temporarily in a firm way and point it to a wall or floor within range. The sensor can point horizontally or vertically for the calibration but should not shift.

You will need a tape measure to measure the true distance of a distant surface during the calibration. If the offset correction is not needed, no tape measurement is needed during calibration and the sensor will deliver correct relative changes after calibration.

5. Power the sensor and connect it to SenixVIEW. In Sensor view you should see a measurement of approximately 7 inches indicating the RT is being detected.

    • Range MIN must be less than 7” at this stage to see the RT
    • If the distance shown is larger than 15” the RT isn’t being detected. We will continue into calibration anyway
    • Make Range MIN 15” by changing the Range MIN value in Workspace and uploading to Sensor. This blanks the RT from detection.
    • Distance now shown should be about correct for the wall or floor surface you are using. The Echo Strength indicator should be about mid-range and blue. If the Echo Strength indicator is red or the distance indicated is obviously incorrect, continue to step 6c.
    • If Echo Strength is red, no wall or floor surface is detected, click Workspace > Measure and choose Free Air Medium or Free Air High. Enable Far Range Gain Boost. Click OK and upload Workspace to Sensor. If the wall surface is detected, proceed to step 7.
    • If Echo Strength is blue but weak, click Workspace > Measure > Advanced and change Starting Gain from 0 dB to 6 dB. Click OK,  Exit,  and upload Workspace to Sensor.
    • The wall or floor test surface must be detected to calibrate RTTC

Activation and Calibration

6. Click Workspace > Measure and choose Reference Target in the Temp Compensation drop list.  A Reference Averaging field opens, selected ON. Click OK and move Workspace to Sensor

7. A notice will appear that making certain changes can affect the sensor’s calibration so a fresh calibration should be considered if changes have been made. For first activation it is required, and SenixVIEW indicates 0.00 for a measurement.  Two new boxes have appeared on the Sensor view, one marked R and one marked U. The R box will be RED at this stage.

    • Two Echo Strength indicators now show. On the left is the RT strength and on right is U (user target) strength

8. To enter calibration, first you must be in Sensor view. In the Sensor drop menu choose Reference Target calibration. A new dialog box opens for Cal step #1 for the RT.

9. An Echo Strength indicator should be green and a target distance showing in the lower left window. If no RT is found, uncheck                the limit range checkbox. If the target is outside a range of 6.00 to 8.00 inches, unchecking the box will allow it to be detected.               Be careful it isn’t detecting the far User target surface.

    • If no RT is seen, raise Starting Gain to 6dB or higher. Click Reset to refresh statistics windows. Look for a small range, zero errors, and Std Dev of less than 0.004 indicating a strong steady RT. It is essential the RT is steady, seen as low Std Dev. If not steady, raise Starting Gain some more, click Reset, note improvement. When ready click Go to Step 2 for the User target acquisition and offset.

10.  Cal step 2 shows the distant U target strength and stability. The Echo Strength indicator is much more active. Click Reset several times to let it settle. Look for a small Range and Std Dev and zero errors, using the image as a guide.

11. Offset adjustment is optional for applications needing absolute distance as well as relative change in target position. Using a tape measure, measure the true distance to the wall or floor from the sensor face. Use the up and down arrows in the Cal window to adjust the distance value until it shows the true distance. Use Reset to assist it to settle at the desired value.

    • When the true distance shows, and the range is small and Std Dev small with zero errors, calibration is complete. Click Finish.

The Sensor view has now got two green boxes marked R and U. These indicate echoes are detected from both targets each measurement. Echo Strength indicators also show both echoes in green. If a reference target is lost the R box goes red and the sensor would use the last measurement of the reference target held in memory until it has been restored. No compensation for changing temperature is done when the R box is red.

RTTC is now active and calibrated. It will produce distance data without lagging compensation as air temperature changes. Its purpose is to give correct data of a variable liquid level or other target object, unaffected by warming of the sensor body or by rapid air temperature changes that occur such as when the sun rises or sets at a location.

To stop using RTTC go to Workspace > Measure > Temp Compensation and choose another compensation technique or choose None. Remove the RT from the sensor or increase Range MIN to blank and ignore the foreground reference target.

Repeat the calibration if the sensor is altered or replaced. Calibration can be done in the field and at any temperature using SenixVIEW. All that is required is a tape measure, and that is only if absolute measurements are needed. Otherwise no offset correction is necessary, and the sensor will correctly show relative changes in position of the target object. Use the Chart and Statistics tools to view stability.

Sensor view showing RTTC active and good echo indications. Setup also indicates a 4-20mA output plus one switch output active, with the rectangular rear LED of the sensor set to indicate presence of the reference target.