The MultiTrode Probe has proven to be the most reliable and cost-effective liquid level sensor available.

How Does the Probe Work?
The Probe works by using the conductive properties of the water itself to complete a circuit with a controller. It’s mounted near the inflow, allowing the turbulence to keep it clean. Even if a build-up does occur it’s usually conductive (in wastewater) and so the Probe keeps right on working. When cleaning is required, the probe is installed off a mounting bracket that includes a cleaning device.

Why is it so reliable?
Ultra-reliable! No electronics and no moving parts means there is nothing to fail. That’s why it has a 10-year warranty! No other liquid level sensor comes close.

Why is it easier to install than other level devices?
All you do is hanging the Probe on its own cable into your wet well, using the bracket we supply. Installation is simple – any one of your technicians could do it in an hour or so. What’s more, you install the Probe relatively low down in the wet well. Compared to ball floats, it allows the well to be cleaned out more thoroughly. That means less debris build-up, odors and pump clogs.

Key Features

• Virtually no maintenance required
• Simple installation from outside the sump
• Easy visibility of start and stop points
• Unaffected by fat, oil, grease, debris and foam
• Excellent in turbulent sumps
• Safe, low sensing voltage
• Comes in a variety of lengths with 10-sensors, 3-sensors or single sensor.
• Custom sizes also available. 

Read more…

In the well Level Sensing, lift station, probe, wastewater, water

A variable-frequency drive (VFD) is a system for controlling the rotational speed of an alternating current electric motor by controlling the frequency of the electrical power supplied to the motor. Variable-frequency drives allow operators to fine-tune their processes while reducing the cost of energy and equipment maintenance. 

VFD’s are quite useful to the water and wastewater industries because they can be used with the pumps, conveyors and drives involved in pumping and aeration applications. For instance, pumping uses excessive energy and cause significant wear-and-tear on equipment. Use of VFD drives enables pumps to accommodate fluctuating demand, running pumps at lower speeds and drawing less energy while meeting demand.

MultiTrode has developed an innovative VFD algorithm which makes it very easy to setup a VFD station. The standard application uses one 4-20mA control loop through each drive. The MultiSmart Pump Station Manager algorithm then provides a smooth power curve as levels are increased and decreased regardless of how many pumps come online.

For example, the lead (duty) pump starts at 50%, and at the level where it is running at 100% the lag (standby) pump starts. A lot of applications would start the lag pump at 50% and keep the lead pump at 100%. What the MultiSmart VFD algorithm does is start the lag pump and bring the speed of both to 75%. (And note that all of these parameters like start speed and level for 100% speed are user adjustable)

Therefore, multiple pumps will always be running at the same speed, and the speed will be adjusted depending on how many pumps are running.

Setup of this module is simple, with only the following values needing to be setup for each pump:

• Start speed, %
• Level at 100% speed

Some additional features help to optimize the station:

• Manual (hand) speed (to ensure that pumps run at full speed for manual/hand mode)
• Fixed speed value and duration if required, e.g. to clear pipes by running pumps at 100% for 10 seconds initially

Read more…

In the well MultiSmart, pump station, Variable-Frequency Drives, VFD, wastewater, water

Drawings of new pits come through my desk nearly every month and most have the MultiTrode Level Sensing Probe already specified, but from time to time I see a ball float right at the top to indicate high level and an alarm. The following figures show the backup level sensing configuration with a ball float and how that configuration matches with the backup Fail Safe Probe sensor design.
 

Proposed Tank Level With Ball Float

Proposed Tank Level With Fail Safe

It seems no one ever thought of changing the ball float to a new and more advanced Fail Safe Probe and install the Fail Safe Relay as well. Ball floats have their place; but when mission critical high level flow’s need a mission critical alarm, a Fail Safe Probe is the best bet together with a Fail Safe Relay.

Those who are familiar with the probe would know that the 200mm single sensor probe has just one wire, but the Fail Safe has two. The Fail Safe Controller will “integrate the loop” to check for continuity of the circuit; and if there is a break in the cable it will close a relay that will warn that, the integrity of the probe to do its job has been limited or has failed. Handy if you have a sewerage pumping station near a creek or river where people swim a lot. Read more…

In the well, Industry Backup Level Sensor, Ball Float, Fail Safe Probe, Level Sensing, probe

The MultiTrode Liquid Level Sensing Probe hangs in the wet-well by it’s own cable. When specifying the probe, we need to know:

1.       The probe length, which is the effective detection length. Standard lengths are 1.0m (3’), 1.5m (5’), 2.0m (6’), 2.5m (8’) and 3.0m (10’). Custom lengths are also available on request
2.       The cable length, which has to reach from the top of the probe in it’s normal hanging position, to the junction box or control panel.

In most installations, the probe is sized for the “live” depth of the well, the range that the liquid normally covers. The live range is typically only the bottom 25% – 50% or so of the full wet well depth. E.g. if the wet well is 5m deep, but the invert is 3m below ground level, the live range of the well will be 2.5m, so a 2.5m probe will be used. The probe will be hanging from the top of the well, with 2.5m of cable between the top of the probe and the hanging point.

Occasionally however, the probe will be installed to measure the full range of the well, such as when it is a back-up to an ultrasonic sensor. The top of the probe will be close to the mounting bracket, so an installer may think to pull the excess cable back through the conduit so that it is not hanging in the well, as shown in the first photo. The probe rarely needs cleaning, as the turbulence of the inflow cleans the debris off the probe (as seen in the first photo). However, if it does need cleaning, the method is to simply pull the probe up through the cleaning bracket, as shown in the second photo. This will require slack cable between the conduit entry and the top of the probe, equivalent to the length of the probe. The probe in the first photo cannot be cleaned in it’s current state. Cable will need to be pulled back through the conduit, and hung looped from the mounting bracket.

Probes are supplied with either 10m (30’) or 30m (100’) of cable as standard, longer lengths are available on request (but will incur shipping delays). If in doubt, it is better to have 19m too much cable than to have 1m not enough!

Probe installed without sufficient cable to facilitate lifting out of wetwell for cleaning.

Probe being cleaned.

In the well probe, probe installation

An almost universal rule of lift stations is that the engineer designing the lift station does his calculations and adds a safety margin. He or she passes it to someone else in the organization who adds a safety margin. Then it goes back to the city for approval and they add a safety margin.

Finally, there is always the chance that when the PO is with the supplier, he or she says “sorry, we’re out of stock of that model, but I have the next size up – tell you what, I’ll sell it to you for the same price as the smaller pump!”

The net result is pumps which are much too large for the application, running for very short times and not at all at their best efficiency point.

There’s a great article about how VFDs can improve the energy efficiency of pump stations by Joe Evans of Pentair writing for Pumps & Systems. The VFD lowers the effective output of the pump and runs it closer to its best efficiency point.

Another way that utilities solve the practical problem of the over-sized pumps is to add a jockey pump later on. This is a more appropriately sized pump for operation most of the time, with no concerns about worst case inflow condition because the larger pumps will take over.

Some stations are designed like this from the outset – especially stations with infrequent high inflow conditions where the engineer has recognized that large pumps are occasionally necessary but running these large pumps for very short periods is not ideal.

What’s the Lift Station Logic?

The lift station or pump station logic we use in MultiSmart is to group pumps.

So with the case of 2 large pumps and 1 jockey pump, Group 1 would have the jockey pump (let’s call it P1) and Group 2 would have both large pumps (let’s call them P2 and P3).

Group 2 would most likely be set to alternate – and it could be set to alternate based on efficiency to save energy automatically. Group 1 doesn’t need an alternation scheme because there is only 1 pump. (If there were 2 jockey pumps they would probably be set to alternate as well).

We configure the setpoints of P2 and P3 above the jockey pump, P1. And we set a parameter called Max Groups Running to 1, and Block Running Pumps to True (which is the default).

Now what happens is the level rises and P1 starts. The well empties and P1 stops. And the cycle continues. But once a time is reached when P1 can’t handle the inflow, the well level will keep rising and the start point for the lead pump in Group 2 is reached. When that happens, Group 1 (which just contains P1) turns off and the lead pump in Group 2 starts.

So long as this large pump empties the well, once the stop point for the lead pump is Group 2 is reached, Group 1 will again take over again from Group 2.

Depending on whether you have Duty/Assist or Duty/Standby you would set Max pumps to run in Group 2 accordingly. If you want both pumps to run together you don’t have to change the default (no limit), if you only want one pump to run, then you set Max pumps to run in Group 2 to 1. It’s an important point because a lot of stations don’t have the pipework to handle both pumps running together and all you do is double the energy consumed for a 10% increase in flow.

The way the logic works if Max pumps to run =1, and the level for the lag pump is reached, is the running pump stops and the other pump takes over.

Technical Note

The way the logic works by default, in high inflow conditions, the jockey pump, P1, will start each cycle, and then the larger pump will take over. If you don’t want P1 to always start, add some custom logic in IsaGRAF, or the logic engine. That logic would be very simple – once Group 2 starts, hold out Pump 1 (or Group 1), and then when the calculated inflow drops below a certain value, remove that hold out fault.

Summary of Configuration

Create a 3-pump station using the setup wizard
In Settings – > Alternation & Grouping:

• Create a new group
• Move P2 and P3 into Group 2
• Check Group 2 is in “Alternate (Std)” – the default
• Check that Group Alternation is “Fixed (Std)” – the default

Configure your setpoints as you want through Settings -> Setpoints -> Level/Control Setpoints
If you do want only one of the large pumps to run at one time, configure Max Pumps to Run in Group 2 – Settings -> Advanced – > Pump Control -> Group -> Group 2 -> Max pump running Read more…

In the well efficiency, high inflow, lift station

In Florida, and probably in lots of other areas that face power outages regularly, there are lots of generators on lift stations.

One of the requests we had was for the capability to limit the number of pumps that could run when in generator mode. We incorporated this into the Profiles feature of MultiSmart.

What’s a profile? In MultiSmart, a profile is mainly about setpoints but includes a few other parameters for pump control.

The idea behind setpoint profiles was to make it much easier for a water or wastewater utility to switch between different setpoints at different times or under specific circumstances. There were many requests for changing setpoints at different times automatically, for SCADA control and for operator intervention when on site. In another post we’ll look at spill management using profiles, which is another great use for the function.

Because of the requirement for Generator Profile, or GenSet Profile as it’s known by default in Multismart, we incorporated some pump control functions as well.

• max pumps to run
• max run time
• max off time (usually used for odor control in wastewater, but has other applications)

This allowed a utility to have a 3-pump station where all three pumps could run normally, but under a generator-powered condition they could only run two pumps. It would be just as easy to have a 3-pump station which could normally only run two pumps, but under generator load, only run one pump. MultiSmart simply has a parameter called Max pumps to run which applies to each profile, including the default profile. You simply change the parameter for each profile (or leave it at the default which is “no limit”)

We also setup this profile so that by default the setpoints were a lot lower in the well, but this is easily changed through the setpoints menu.

Changing setpoints on MultiSmart

How do you switch to this profile?

Generally profiles can be switched by:

• Digital input
• SCADA control
• Date/time (there are 4 timers for each profile)
• Operator interface
• Customer logic, e.g. from the PLC extension to MultiSmart

So in the case of GenSet Profile you would probably configure it to become active when the Generator Transfer switch activated.

By the way there are 6 profiles in MultiSmart. Two of them are labelled up already: spill management and genset. However, if you wanted to use profiles and didn’t these you can change them –  any profile can be renamed and configured exactly how you want it.

Can the setpoints be changed via SCADA?

Yes, as well as switching profile via SCADA, all of the setpoints for each profile can be read and written to by a SCADA system.

How do you configure ”Max pumps to run” in a profile & when a Profile will be selected?

Because it’s a relatively advanced feature, not surprisingly it is under the “Advanced” menu. 

Locating the Advanced screen in MultiSmart

 Press Settings – Advanced and expand out Pump Control to select Profiles. Then you select the profile you want to configure and all the options are in there, including the pump control options, selecting a Digital Input on which to make it active or choosing timers.

In another post I’ll look at the Spill Management Profile.

Read more…

In the well generator, genset, profiles, setpoints

We recently did a survey of Florida water and wastewater utilities. Here is the pdf of the survey.

One of the surprising results from the survey was about energy cost and its importance:

The surprising – and encouraging – aspect was that 47% already rated Energy Cost and CO2 emissions as very important. It wasn’t surprising to see that 85% thought that although it would increase in importance, other challenges would still be more important. Challenges like ensuring sewage doesn’t spill out into the streets, that it is properly treated before being discharged and that potable water is supplied to the residents and customers of the water authority.

Perhaps the UK water utilities are fundamentally different because they are so much larger – typically 1000 – 5000 pump stations – and not government owned. Or perhaps they felt that although keeping sewerage off the streets and drinking water in the taps would always be their no 1 priority – it wasn’t their biggest challenge..

 Pump Efficiency

A while ago we did some research on energy efficiency in lift stations and found that pumps can lose a lot of efficiency even in clean water. Obviously wastewater is worse and the level of efficiency loss depends on the kind of material being pumped – if you have sand, grit and rocks going through the sewer main it’s obviously going to be worse. The Hydraulic Institute said:

“A pump’s efficiency can degrade as much as 10% to 25% before it is replaced, according to a study of industrial facilities commissioned by the U.S. Department of Energy (DOE), and efficiencies of 50% to 60% or lower are quite common. However, because these inefficiencies are not readily apparent, opportunities to save energy by repairing or replacing components and optimizing systems are often overlooked.”

Now the reason a lot of water and wastewater utilities have started using the MultiSmart pump station manager isn’t because of its energy efficiency functionality! But the more progressive ones have definitely seen the potential of MultiSmart to reduce their energy costs. As the Hydraulic Institute said, “Because these inefficiencies are not readily apparent..”  – If you don’t know what’s costing you money, where’s the incentive, or even the budget, to start fixing your problems?

More on Energy & Efficiency

There is a section on our website – Energy and the Environment – which has a few references to energy efficiency studies. And there is also a paper in the White Papers section – note that you need to fill in a short registration form to download any of the white papers.

Read more…

In the well

A few years ago, we found that operators in a few wastewater utilities in one state were visiting their lift stations regularly – some once a week, others once a month, to pump the station right down to the snore point of the pump. It was an important maintenance task because pumping the well down as far as possible was a great way to clean out as much of the build up as possible.

The operators here found that the result was more reliable operation of level devices, less pump blockages and less need for frequent visits from the cleaning crew.

That insight led to a simple well clean out function in the MT2PC, and then in a more advanced form in MultiSmart. The MT2PC version just allowed for a periodic pump down, every so many cycles for so many seconds. Customer feedback from the MT2PC feature was that some improvements could be made -which we couldn’t put into the MT2PC - but of course we did implement these improvements in MultiSmart.

How does it work?

The idea is that periodically, when the well level reaches the normal lead pump (duty pump) OFF point the pump down cycle is extended a little.

Optimize Station - MultiSmart

The MultiSmart feature allows the choice of how to initiate this extra pump down – after a set number of cycles (e.g. every 100 cycles), or on a timer. If you choose timers for the well clean out you might set Monday between 8am and 1pm. If it was a very slow moving well and the OFF point wasn’t reached within this time, the well cleanout wouldn’t happen. Normally of course the OFF point would be reached within this time window and so the cleanout would take place - but only once. The advantage of the timer over using number of cycles is that you can make sure it takes place when people are at work – in case there’s a problem.

Should we introduce “Stop on under-current”?

There was a third choice for the well clean out that we think is a good idea but it hasn’t gone into the product yet (as of writing this post) – run the pump on until under-current - i.e. until the pump starts to snore. In a way you can use this already, but you’ll get an under-current alarm!

If you think that this would be a useful feature for you – or you have any other comments about this feature or the practice of cleaning out wells – please comment (below)!

How is it setup?

From the Settings menu, on the first screen you see Station Optimization, select that and  Optimize and you’ll find the well clean out function with all the parameters. You’ll find some other useful features there as well.

Disabling the low level alarm is managed from the level alarms in the advanced menu:  Advanced – Pump control – Well – Well 01 -Level alarm -Low level – Well clean out disabled (check the box). You might have a low low level alarm as well, if you do you should do the same for that alarm.



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In the well