Can I measure -4V to +4V with Analog input of LOGO ?

Hello,

I have got a motor drive which have analog outputs for RPM. I am trying to monitor RPMs clockwise and also anticlockwise. 

The problem I am having is:

0.....+4V for Clockwise rotation of motor - these I can read with my LOGO analog input and convert them to speed

-4V ....0V for Anti clockwise rotation of motor- these My LOGO can not read as they are negative, and my LOGO shows zero

Is there any workaround so analog input on my LOGO can see the range -4V....0   ?

Thanks

Hello,

Maybe there is the way to configure your motor drive analog output? If yes then change from -4 - 4V to 0 - 10V. Like this: 0-5V anti clockwise and 5-10V clockwise, so exatly 5V will be then motor stopped.

ok, I configured my drive so I never get negative values, therefore:

-4000RPM ( anticlockwise).........................0V output

0RPM..........................................................2V output

4000RPM (clockwisee) ..............................4V output

I only use 3500rpm max, clockwise, anticlockwise so I am in range.

Now I am struggling to set scaling of the aplifier block.

The first analog amplifier block i have set succesfully, so I get actual voltage reading on the logo display, so:

Minimum:1

Maximum:1000

Gain:1

Ofset:0

But how do i do calculate RPM?