fuelish questions

I have a little experience with the Mitsubishi Alpha series controllers, having programmed one about 3 years ago but I do not do this very often. Here is our situation: We want to control a diesel fuel transfer pump. We have a float switch NO/NC, in a small tank by a generator. When the level in the small tank falls the float switch closes and turns on a pump that refills the small tank from a larger tank. In the pump line there is a flow switch that closes when the pump begins to draw fuel from the large tank. What is the best way to configure the controller so that: a. if the small tank fills up and the float switch opens, the pump turns off. Or b. if the pump jams or the supply line from the main tank breaks and the flow switch opens, it will also turn off the pump. We need to have either switch be able to stop the pump indepenently of the other. The pump is interfaced with a standard motor starter. Thanks, Ken

I am not familiar with the alpha series. This would be ideal for Moellers "easy" smart relay, or one of the many others that relabel the “easy”. Most small smart relays have 4 inputs and 4 outputs, minimum, and may be cheaper that your plc.

You would have four inputs:
1). Manual switch contact (N.O.)
2). Automatic switch (N.O.)
3). Float switch – contact closes on demand
4). Flow switch – contact closes with flow

Your outputs could be
1). Motor starter
2). Alarm light or horn
3). Remote alarm contact
4). Spare

I used to design and assemble day tanks. This is a pretty common circuit, generally using relay logic. I can draw this, program this, but am having difficulty typing it into verbal ladder logic. Have to leave now, so will post logic later on.

Regards….casey

Now, an attempt to cut and paste MSWord ladder logic programmer


MOTOR OUT RUNG

.....AUTO…......FLOAT…......FLOW.........MOTOR.OUT
-----[ ]---------[ ]---------[ ]-----v-----( )-----
-----[ ]---------[ ]---------[ ]-----^
.....AUTO.......FLOAT.......TIMER



TIMER RUNG

.....AUTO.......FLOAT.......5-SEC
-----[ ]---------[ ]-------{TIMER}-----




ALARM OUTPUT RUNG

.....AUTO.......FLOAT….....MOTOR.OUT.....ALARM OUT
-----[ ]---------[ ]----------[/]-----------( )-----




TEXT EXPLANATION


MOTOR OUT RUNG

IF Auto is ON, IF FLOAT is ON, IF FLOW is ON, THEN MOTOR is ON
OR
IF Auto is ON, IF FLOAT is ON, IF TIMER is ON, THEN MOTOR is ON


TIMER RUNG

IF Auto is ON, IF FLOAT is ON, THEN TIMER is ON for 5 seconds
5 seconds being random, guessing that you could have fuel flow that fast


ALARM RUNG

IF Auto is ON, IF FLOAT is ON, IF MOTOR is OFF, THEN ALARM is ON


REMOTE ALARM RUNG
Same as alarm run, except going to Remote Alarm Output coil


Hopefully you can understand it a little clearer than mud. This could be made fancier, have lockin or lockout coils, silence button, etc. But here is the basic idea.

Any questions, make a post, or PM me.

Someone else will probably have a different way of doing it. I could do it relay logic style with one timer, and one or two relays, epending if I wanter to lock it out on failure. Once again, an ideal application for a smart relay.

regards.....casey

Hey Mr. C, I really appreciate your efforts and thanks for sending me the ladder logic. As I said, I can go for a couple of years or more before I ever touch one of these puppies but then, occasionally, the need arises and I start scratching my head trying to remember what I did. The Mits software for the Alpha is all graphical and uses function blocks that enable you to piece the signal flow and control functions together. I managed to stumble through it and get a configuration that works. If it has a function that allows me to print out what I did in ladder form then I will post it. Since this is what I know best I'll use another Alpha "simple" unit for our application.

I have never worked with the ladder format before but have something called "ladder builder" that came with a Keyence controller that I had to reprogram a few years back. I plan to dig into it and see if I can get your suggestions in working form. Lots to learn here, no doubt. I wish that I had occasion to work in this area more than I do. Ken