Step7

We have a Grinder motor that runs constantly to fill up a tank, and a smaller motor to feed the material in the Grinder. What would be the best way to keep up with the number of starts and how long the smaller motor is running? I am trying to find out if it is necessary to run the Grinder motor constantly.

Thanks

First of all I'm assuming that by S7 you mean S7-300 or 400 and not S7-200. In that case this info is no good for you. Since counters react on the rising edge of the count signal, you could use the switching of the motor to count. For the runtime you need the built-in run-time meter systemfunctions SFC2 SET_RTM, SFC3 CTRL_RTM and SFC4 READ_RTM. Check the help file for more info.

Kind regards,

Constantly run the smaller feed motor?

Hello Guest,

From the way I interprete the application you are trying to find out if it is necessary to run the smaller Feed Motor (not the Grinder motor) constantly.

I am assuming the smaller motor feeding the material to the grinder was driving a screw feed conveyor. I am also assuming that there was a current indicator on the control panel with a high and low current switch setting on it to start and stop the small feed motor.

I think the smaller feed motor was design to feed the material faster than the grinding speed and therefore the smaller feed motor will always be on a start/stop operation unless it is variable speed controlled.

But I also think that the best throughput can be achieved when the feed motor was running constantly.

Can use auxiliary contact from the smaller feed motor contactor as digital input to PLC to count the number of starts and activate an elapsed timer programmed on the PLC.

Just trying to help!!

Regards,

Vic Jasareno

Anyone have an example of a run time meter?

Thanks

guest,

Sure, a run-time meter would be just be one ladder rung: a PLC Input (that is physically wired to your motor starter or "Run" switch, and the Timer that starts and stops when the motor starts and stops. Like this:

|. . . . . . . . . . . . . +-RTO-----------------------+. . . ..|
|. . . . . . . . . . . . . .|. .RETENTIVE TIMER ON . .| . . . .|
|. . . . .I:1/0. . . . . |. Timer. . . . .T4:0. . . . . . .| . . . .|
+-------| |----------|. .Time Base 1.0 sec. . . . .|------+
|. . . . . . . . . . . . . .|. .Preset. . . . .32767. . . . .|. . . . |
|. . . . . . . . . . . . . .|. .Accumulator . . .. 0. . . . | . . . .|
|. . . . . . . . . . . . .. +----------------------------+ . . . .|
|

When I:1/0 is ON, the timer will time until motor stops, and then restart at same time for the next start. If you need more than 32767 seconds total, then use two or more timers, with the second one counting minutes, and so on. On most PLC's there are also built-in clocks that can also be used for timing functions.