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|September 1st, 2008, 10:45 PM||#1|
Join Date: Sep 2008
Using the Analog output from a VFD to display RPM on HMI
I am new to programming Analog inputs and am wondering how to use the analog output from my inverter drive to an analog input on the PLC. Then output a RPM display to the HMI.
I am using a Hitachi L200 drive. The motor base specs are 200-240/460VAC, 3phase, 2HP, 1800RPM. The PLC is an Automation Direct DL205 with a D2-260 CPU. The drive outputs 0-10V depending on the Hz.
The motor turns a spindle through a belt drive, and the spindle has sort of saw blade mounted to it.
How do I convert this Hz output into RPM to display?
|September 1st, 2008, 11:42 PM||#2|
Lifetime Supporting Member
So at 30 Hz, the motor is at 900 RPM etc. Basically, Motor RPM is Hz * 30.
Next, you have to take into account the belt drive unless the pulleys are exactly the same diameter. If they are not, you have to multiply by the ratio of the pulley diameters. If the driving pulley is smaller, the output RPM will be smaller if the driving pulley is larger, the output RPM will be larger. So, if you have a 10" pulley driving a 12" pulley the speed will be reduced by the factor of 10/12.
Now the fun begins...
You have to find out how many Hz is represented by 10V. For that drive, 10V equals whatever the programmed Maximum Hz is. The default is 60Hz for US drives and 50Hz for European drives but someone may have changed it so you have to check parameter A004.
BUT.... I'm pretty sure that output is not a true analog output, it is a PWM output that will drive an analog dial gauge just fine but may cause havoc with an analog input on a PLC. If the analog input is fast it will see the separates pulses instead of the simulated voltage. I've never tried it but there may be a way to design in a capacitor across the terminals to make an analog input read the signal. You could look into this: http://www.ontrak.net/pwm.htm
So say you overcome that Hurdle. Then you have to have an analog input in the PLC that will accept 0-10V and turn it into a number. You have to check the manual for the I/O card to know what the number is.
Let's say for example that your 0-10V becomes 0-32767.
Then let's say your drive Max Frequency is still set at 60Hz and you have my 10" and 12" pulleys installed. With that reduction, the drive 0-60Hz has a spindle speed of 0-1500 RPM. Then, for this example the number 0 at the input would be 0 RPM and the number 32767 would be 1500 RPM. Everything else is linearly scaled inbetween. I don't know AD controls so they may have a block to do this or you may have to use a little math.
Hope this helps
nOrM=Norman Dziedzic Jr.
Your program may do things you never intended/ When the inputs are in a state you never expected.
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