Current Sensor

We are working on current sensor acs712.
We are facing a problem in using it.
We connected powersupply, multimeter, current sensor and load on series.
Whatever may be the input voltage the output of current sensor is not changing.
Can anyone say why this is happening like this?
Thank you

There is more than one ACS712 sensor, so which one.
The ACS712 sensors I know need a 5volt supply.
The "no current" output voltage is half of the supply voltage.
Your DMM should read ~2.5volt between output/ground, with deviation from that voltage when current flows through the sensor's current terminals. This (DC currrent) has to be a significant portion of the sensor's max rating.
For AC or bi-directional DC, try this:
Make a voltage divider from two equal (~1k) resistors in series, and connect the ends to the sensor supply.
You should now have 2.5volt on the center tap of the two resistors.
Connect the DMM between the sensor output (2.5volt) and the voltage divider (2.5volt).
The DMM should now read ~0volt without current through the sensor.
Set the DMM to 200mV. It should read a voltage with curent through the sensor.
Set the DMM to DC for DC currents, and to AC for AC currents.