Not sure if your sensor is freaking out or you just need to test it's accuracy to see if you need a replacement? This looks like a good tool for that purpose to have in your robot toolbox
https://www.ebay.com/itm/HC-SR05-Ultrasonic-Distance-Module-Demonstration-Board-Tester-Ranging-HC-SR04-/160743462144
nice little find
Lol right after I posted this someone bought on of them. I added pics with a screenshot because eventually that link will expire.
You could buy 15-20 sensors for the price of the tester. If anyone has an HC-SR04 they are also likely to have an EZ-B or Arduino (or something else) which is very simple to just plug and play, which would do the same job.
Personally I can't see the point in it...
For myself I can , you can buy sensors a dime a dozen but some of them come busted to begin with and it's frustrating not to know for sure what's going on or if there is an internment issue. The intermittent ones are the worse. Troubleshooting equipment using "swaptronics" works but you could be throwing away something that wasn't broken. I've considered trying one of the name brand sensors like a parallax to see if they are more reliable or accurate.