Repeated calling a function embedded in an init function

Noobish here.

I am building a raspberry pi project to measure the depth of a water tank every 5mins. I have placed an ultrasonic distance measure in the tank and have got everything running using node and the r-pi-usonic library. I can make an initial call to the ultrasonic device to create an average of 10 individual measures (because of the variability in individual measures) and log that to the console.

But what I want to do is repeat this every 5mins. I initially tried to do this by setting a setInterval(), and have tried using cron. But as the query loop is tied up in the init function, it throws the following error...

timers.js:274

callback.apply(this, args);

        ^

TypeError: Cannot read property 'apply' of undefined

at wrapper [as _onTimeout] (timers.js:274:13)

at Timer.listOnTimeout (timers.js:119:15)

So my question is really what is the best way to get this to run the query every 5mins? The answer will no doubt help my understanding of callbacks etc.. Sorry for being such a dunce!

My code is here, apologies for its crapness!

//Import required modules



var usonic = require('r-pi-usonic');

console.log('starting water tank monitor');

var min_tank = 30

var max_tank = 90

var tank_percent = 0



usonic.init(function (error) {

    if (error) {

        console.log('Error')

    } else {

        var sensor = usonic.createSensor(13, 21, 1000);

        var i = 0

        var values = 0

        function  myLoop (){

            setTimeout(function () {    

                var v = sensor().toFixed(2) ;

                values = values+parseFloat(v);

                i++;                     

                if (i < 10) {            

                    myLoop();             

                } else {

                    value = (values/10).toFixed(2)                  

                    tank_percent = 100 -((value - min_tank )/ (max_tank - min_tank) * 100)

                    console.log(tank_percent);

                    i = 0;

                    values = 0;

                }                     

            }, 500)

        };

    setInterval (myLoop(), 30000);      

    }

});