two tanks control problem

[Farah Badardin]

Hi,

I have been trying to solve this problem for months now. I work as an Electrical Engineer in a tunnel project, we will use TBM machine to drill the underground station.

We just realized that for the new TBM machine that we bought, we actually have 2 tanks of grout component, called component A. The problem is, we are using the panel for old TBM machine where the component A tank only have one.

So, in order to provide additional control for the second tank to the existing control for the first tank, I am planning to modify a little bit of the control circuit where, from the level sensor in the tank, it will send signal to the PLC in the panel. This PLC will send command for the valve to open, and hence will make the pump runs.

We do not intend to modify any coding in PLC since it was done by a subcontractor. What we can do is only mechanical modifications, where my boss gave an idea to use a simple relay. He asked me to crack down on how to implement it, maybe using 4 poles relay, but until now I still can't figure it out.

I was trying to implement the simple basic start and stop pushbutton circuit, where I try to manipulate the start and stop pushbutton by changing it to high and low signal from the level sensor, but the problem on how to connect them to PLC still cannot be solved, since we need to integrate two signals from two level sensors into one slot of PLC, and from one slot of output PLC to command either two valves to open.

 

[dmxtothemax]

If you make tank two exactly the same size and capacity as tank one,
Then just connect them together, then you will not need extra control gear, because both tanks will have simulair amounts in them.

 

[static zap]

Tanks running in parallel = faster flow !
Tanks in series .. one after other with a change-over.
(of both pump control and sensor )
Longer run time ... Has system got a continuous rating , or is hard-ware meant to be rested (Duty cycle) ?
(Guarantee voided as will show up in a log somewhere)

 

[Bobster]

If this is the standard of "engineer" we are using on the UK underground network I worry.

 

[Spoon]

If this is the standard of "engineer" we are using on the UK underground network I worry.

The OP is based in Kuala Lumpur..

 

[Bobster]

In that case, a software modification would take about an hour and see the job done properly.

Call the subcontractor back in.

 

[Spoon]

All depends on the cost of altering the software. Back in the days, when we had someone else doing some software, they used to charge us 3 grand just to do a small change.

Not quite sure what the OP is after. I think I'm reading it wrong. Can you please go into more detail about how the current operation works.
There has got to be more to it than a level sensor that wires to PLC input & an output from the PLC which activates a pump.
You could do this operation just using relays.

 

[Wilko]

Hi - appreciate your Boss has sent you on a mission, but I am with Rob post #6 on this - if it's designed to be software controlled, that's what should be done. What if your new relay dies and the pump fails to start or stop when it should? Could be a big "oh dear" moment when you're in a tunnel, just saying.

 

[Farah Badardin]

If this is the standard of "engineer" we are using on the UK underground network I worry.

Well I don't know how work environment in UK is but in my place, when a new engineer is not knowing something and asking question about it, they will offer helps without being judgy.

 

[Farah Badardin]

All depends on the cost of altering the software. Back in the days, when we had someone else doing some software, they used to charge us 3 grand just to do a small change.

Not quite sure what the OP is after. I think I'm reading it wrong. Can you please go into more detail about how the current operation works.
There has got to be more to it than a level sensor that wires to PLC input & an output from the PLC which activates a pump.
You could do this operation just using relays.

You are correct. That is why we dont really want to ask the subcon to make changes (that would be the last resort if nothing else can be done) because they would charge a lot more for it.

The control of the tanks is connected from tunnel to surface. So on surface we have one grout plant that will receive signal from tank in tunnel whether the grout needed to refill or not. The existing control for refilling the tank is only for 1st tank only while the 2nd tank is the new addition added by the TBM supplier.

 

[Lucien Nunes]

There must be a reason for the new TBM to have two tanks, so the programming would reflect how they are supposed to be used. E.g. to allow a minimum agitation time, or a maximum open life of the grout component, in which case it would draw from whichever tank has material in the correct state rather than both at once. Or as DMX says, it might be intended to draw from both for maximum flow rate, and keep them at the same level, and there are only two tanks because they are easier to make than one big one. We don't know any of this so we can't suggest a work-around. Nor do we know what the PLC does under error conditions, e.g. what happens when the 'low' level is continuously detected. What should it do if one tank is high when the other is low? Is that an error condition in its own right?

So this seems to be beyond the scope of simply switching the PLC's inputs and outputs from one tank's sensors and valves to the other. If you are completely familiar with the process and you know that it is possible to just choose one tank manually, then you might be able to fool it by switching CR1-3 and X37-38 between tanks, but beware creating error conditions if for example the PLC detects an impossible transitional state during the changeover, e.g for a moment both high and low levels are detected.

I'm with Rob, get the programming altered!

 

[Deleted member 26818]

If you join the two tanks together at low level with some large diameter hose, you would only need the one level gauge.

 

[littlespark]

If something goes wrong with this thing, you want the buck to stop with the supplier/programmer of the machine, not you.
Get it done by the right people.

The extra costs now will be outweighed significantly by downtime if theres a breakdown.

"who altered this?"

Everyone points at you

"why did you do it like this?"

"Um..... I asked on a UK based internet forum"

 

[marconi]

'
The Bitterness of (a) Poor Quality ( proper solution) remains Long after the Sweetness of Low Price is Forgotten.'

The Bitterness of Poor Quality remains Long after the Sweetness of Low Price is Forgotten. - https://www.elephantjournal.com/2013/04/the-bitterness-of-poor-quality-remains-long-after-the-sweetness-of-low-price-is-forgotten/