Functional Description and Factory Acceptance Testing

Well it has been a while since the last post and I thought we will kick off this post on the above topic. We may have touched on this in the past, but we will look at a bit more detail and how to draw up the documents.

Let’s start with the Functional Description (FD) and what it is. To keep it in plain English, it is an exact description of how the installation needs to operate. It will state the sequence of events for the electrical circuit. If we use a very simple example of a pump, a modulating valve and a level control in the tank, we can write it as follows:

The pump will start on Low Level

On low level, the modulating valve opens to 100%

At 50% level, the modulating valve closes to 50%

Should the tank level remain at 50% for longer than 3 minutes, modulating valve opens to 75% and remains there until level reaches 70%. At 70% level, it will close to 50% again

At 90% level, the modulating valve closes to 95%

At high level, valve closes 100% and pump stops

Just a word of caution, the statement above is not from an existing system. I have just put any condition in to show how we derive the two documents from the operation of the system

With the FD written, we will now create the Factory Acceptance Test Report (FAT Report)

Each one of the conditions in the FD becomes a test point on the FAT if that makes sense.

How you set your document up is dependent on the requirements from the client or yourself. It makes sense to put it into a table format.

Level Valve Position Pump Running Signature Date
Low 100 Yes    
50% 50% Yes    
50% >3 minutes 75% Yes    

 

Keep adding to your FAT for every condition that is to be met. Test the system, record the findings and sign off as tested. The above is a very simplified method and these could be very large documents for big projects. The point is, the methodology remains the same. Draft your FD and derive the FAT from it. Capture every test point including alarms, fault signals etc.

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Electrical Contractor?

Time for another post but this time we will take a look at something entirely different. Quite often we tend to venture into our own contracting business thinking that we will be able to get out there, do a good job and at the same time make a healthy profit on our work. Absolutely nothing wrong with that, the problem lies in how we go about running the business

In our industry it seems to be the norm to set up a business and immediately start cutting our competitor’s prices in order to win the job right? What you need to ask yourself is the following:

What does it actually cost you simply to run a business? In other words, your true overhead costs.

Why on earth would you want to be working at the lowest rate around? When employed full time, don’t you try to earn more?

Have you got the resources to be delivering what you promise your clients?

Let’s start by looking at the cost of being in business.

First, your salary! Include here your salary, pension/super contributions, medical cover, insurance payments etc.

You need an office to work from (most will start by working from home)

You need office supplies, telephone and a PC with a decent printer.

You need a reliable vehicle. Now here is where I tend to have a bit of a different view. Your vehicle portrays the image of your business. It needs to be clean, in good condition and suited to your work and lastly, signwriting! This is important. Everyone that sees your vehicle could be a prospective client so make sure it looks professional. Don’t think that because your vehicle is paid for you do not need to include a figure for it. The truth is that you need to be able to replace this at some stage and it needs to be calculated into your costing.

Traveling Cost. Where is the bulk of your work likely to be, how much fuel would you be using to get to the jobs? These are all items that you need to be estimating and taking into account

 

Tools and equipment. True, you need basic tools to get started but you need to ensure you have the right tools for the right job, and anything that will make the job quicker and/or safer is a must.

So, by looking at all of the above, calculate your cost/month. Take this figure and work it back to an hourly rate. This hourly rate is the bare minimum or break even rate. If you are willing to work for this rate, you may consider finding a full time job with an employer again.

This is where a lot of us would go wrong. We see this rate, it could be $55/hour, and we think that is a lot of money as it is way more than what you earn as an employee right?

What you need to consider is that you may have weeks where you do not have a guaranteed 40 hours of work and someone needs to pay the bills. The reason you run a business is to show a profit. That is why we have a profit margin on top of our rate that we must calculate. Your competitor needs to do the same. To be honest, I would rather not have enough work than working at a loss on a job.

That is enough for this post. Calculate your cost and see where you are positioned with your business. Next time we will have a look at how you need to plan your material purchases etc. Until then, have a wonderful weekend and remember, always put safety first.

By the way, if you have not got a copy of my book yet, head on to www.lulu.com/spotlight/SparkyHelp

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Using The Alpha Controller

In our last newsletter we had a look at the Alpha Controller and some of the functions. This time, let’s have a look at a possible application of the unit.

You need to monitor the runtime of a motor which is supposed to run for a maximum of x seconds (x = time you want the motor not to exceed) Should the motor exceed this time, you want to force it to stop and lock it out to prevent a restart without physically resetting it. At the same time, you want to be notified of the fault.

Let’s start with the inputs you will need.

1                    “run” signal. This could be a normally open contact on the motor contactor

2                    “reset” button. This is the physical reset button that must release the fault lock-out

 

Now we will look at the output side. This is a rather easy one as we will be using one output only. This is the relay that will need to lock out the motor in the event of it exceeding the run time. We will simply connect the motor control circuit via this relay. That means when our output is on, the motor is stopped. This is one area where we need to pause and consider the application. We assume that this is not a critical application and that no damage would arise should the lock-out fail. If this is a critical application, we must ensure that we wire our circuit to “fail to safe” in the event of a power loss. Simply put, if we do not want to energise the relay for the fault condition but de-energise it. We will discuss that more in future

 

Back to our circuit. When we receive the input to tell us the motor is running, our timer will start counting. This timer is set to the maximum time we want the motor to run. If we exceed the time, we turn on a set coil, activate the display screen as well as a second timer. We will discuss the function of each separately.

 

Set Coil. This coil will turn on and remain energised even when the input to it is removed. The only way to de-energise this is to provide an input to the Reset which is provided by our reset button

Display Screen. When the screen is activated, it will display the message you set up. In this case we right click on the block, select open parameter dialog and click on the string radio dial. In the text box we will enter the required message. Lower down you will see the text x and y co-ordinates. Use these to set the start point of the text. You will also note that you need to set the length of the text.

Delay Timer. This timer is put in just to allow the screen to display the correct text before the GSM modem sends a sms for the alarm. Without this slight delay, you could get a message that only shows input/output status and no text.

 

Have a look at the screenshot below and write the program. Select the simulation mode and have a look at how it works, then improve it. Please note that this program was only set up as a tutorial. If you want to use it, please test it and ensure you take into account all safety precautions

gsm

Till next time, stay safe and remain passionate about your work. By the way, for those who have not had time to get their copy of the Manual for Electricians Volume 1, check it out on www.lulu.com/spotlight/SparkyHelp

 

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Basic Electrical Circuits: two way switching

Thought I will get the post in a bit early this week. As with the previous post, please click on the link below to view the post.

Hope you are having a great week!

Basic Electrical Circuits D2

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Basic Electrical Circuits: Light & Power

Time for a new post and this time we will do a little bit on the domestic type installations again. You may need to click on the topic to open it as There are quite a few sketches this time which makes it a bit harder to post. Hope you enjoy it!

Basic Electrical Circuit light & power

Just noticed the red lines went missing. The document below has the sketch with the red lines as mentioned in the post.

sketch 1

 

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Programming With Logic

Using Logic Blocks to Program

 

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Fault Finding Electrical Circuits: Logic

Time for another post and I think we should touch on this topic again; using logic when we have to fault find a circuit.

Before we go on, just a reminder; if you have not had time to check it out yet, don’t forget to get your copy of: Manual for Electricians Volume 1. Find it at www.lulu.com/spotlight/SparkyHelp

1                    What is Logic?

The reason for this question is quite simple: In order to troubleshoot an installation/machine, you need to be able to think in a logical manner. So what exactly do I mean by that? Let’s have a look

We have a machine that is made up of a conveyor that moves a box to a specific point where it is pushed off the conveyor by a pneumatic ram. You are called to site as the machine has stopped working. When you arrive, you are shown to the machine and the operator tells you what is supposed to happen and then walks away. As usual, there are no schematics available.

Now, logic tells me that in order for the box to be pushed off the conveyor there are two essential components required:

  • Some kind of sensor to detect the box
  • The solenoid that needs to activate the ram

So without having access to a schematic diagram, we have established what needs to be there for the machine to function. That is Logic! You will also notice that we have not opened the door to the control cabinet yet. At this point I am not concerned with what is in there at all. It could be some relays or a PLC. It does not matter at this point. The only thing I am now concerned with is what makes this machine work downstream.

What we need to be able to do is to look at a machine and understand how to piece the different functions together to form a snapshot of field devices and operational sequences. Once we have this, we can move to the next step

 

2                    How do we Use it?

I recommend you always have a notepad and pen as part of your toolkit. Once you have had a look at the machine, draw a simple flow chart to indicate the operation. Let’s have a look at the following:

Sensor:            24V DC Proximity

Ram:                24V DC Solenoid

 

What I will do now is to put a box on the conveyor and run it to see what fails. Let’s assume the box moves right past the sensor without the ram pushing it off. We know the conveyor part works so we have only two things to check. The sensor and the ram. Most sensors have an indicating lamp that blinks when it detects the object, but we will assume this one does not. So how do we proceed from here? Simple, we use logic once again. Consider how a solenoid operates. It is a coil that will create a magnetic field when energised. So if the solenoid is being energised, we should be able to detect that at the solenoid as follows:

Place the tip of a non-magnetic screwdriver on the top of the coil where the locknut is. If there is power to the solenoid, the magnetism will hold down the tip of the screwdriver. You check this by lifting the screwdriver softly away from the coil. If it is energised, you will feel how the magnet holds it.

Great, we have power to the solenoid which means the sensor works and there is power to the solenoid so it is not an electrical fault. Now we can walk away from the machine and leave the client without his machine because the fault is not on our side right? Sorry, this time the answer is no!

 

If we have established that there is power to the solenoid, we know that the fault is on the ram. It may be as simple as an airline that has been turned off. Do a quick check to make sure you have air to the actuator. If you have air and power, then you may need to call for mechanical assistance.

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Fault Finding Techniques

Hi All. It is time for another post and it may be a good time to link the PLC into the circuit to see how it will affect your fault finding skills.

As the PLC becomes more popular on an installation, it is necessary for us to have a better understanding of what to do when something goes wrong. What I would recommend is that you set up a list showing you exactly what is connected to the different input and output terminals of the PLC. Let’s create an example:

Digital Input Device Description
00 Limit Switch Hydraulic Clamp   Open
01 Limit Switch Hydraulic Clamp   Closed
02 Pushbutton Start
03 Pushbutton Stop
04 Overload Thermal Overload   Normally Closed Contact
05 Overload Thermal Overload   Normally Open Contact

 

I have just set random inputs up here with no thought of a program just to give you an idea of what I mean. By having these set up in a list, do the same with all of the outputs. Create a functional description of exactly how the machine needs to operate. Make sure you look at sequences and interlocks. In other words, the hydraulic clamp must be open before the conveyor can run. By simply having that information and the input number of the limit switch that is going to provide the signal, you can trace the circuit.

If the clamp is in the open position, the limit must be activated and as such you will see the input 00 light on the PLC turn on (should the PLC not have an indication, you can simply test for voltage on input 00 to determine if the limit switch is providing the signal)

We are only just scratching the surface here. What you need is a full functional description that will include every input and output connected to the PLC. Armed with this, work your way through the sequence; one input/output at a time. What is also very handy to have here is to make a drawing of the installation. In other words, show every single device as it is installed. This together with the description will make it easier to understand how it is meant to operate. This is where logic plays a big part. You will need to understand the process when you look at it. The position of limit switches, sensors and any other field device will aid you to understand it.

Looking at the installation, you see the limit and ask yourself why it is there. Use the example above and ask yourself what would happen if the conveyor started with the clamp in the closed position. The consequence of this will tell you that it must be open otherwise the load will not be released and will cause a “jam” on the conveyor. This is how you get to understand the machine. These devices almost need to “talk” to you when working through them if you understand what I mean. I know I am trying to give you a lot of information in a very short post, but hopefully this will help you to work past the fear of seeing a PLC in the cabinet because you don’t have the software for it.

Till next time, you guessed it by now but still, work safe and always consider others around the installation you work on. Have a great week!

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Fault Finding

Came across a different motor the other day and thought this may be useful. Even though I decided to throw this in under Fault Finding, it is more a motor connection topic. Reason for me putting it here is that I happened to walk in when the motor in question was being tested.

On starting the motor, it made a very load “growling” noise which drew my attention straight away. When asking what was happening, I got told the motor is drawing in excess of 80A. The full load current of the motor should be 9A. This prompted me to do a quick test on the motor as the sound I heard told me we had one of the following issues:

  • Reverse Winding
  • Open circuit on one winding

Reading the manufacturers plate told me we had a different issue as the motor windings are made up of 6 different windings. These motors were designed for different voltage applications. We were applying 415V to it and it became clear to me that there must be a wiring issue. The windings were labelled as: U1, U2, U3,U4; V1, V2, V3, V4; W1, W2, W3, W4

Opening the terminal box, I found 6 terminals which means that certain windings were bridged. Let’s have a look at the description on the nameplate and then we will look at the terminal box and how it was to be connected.

Nameplate

Looking at this sketch, we will note the bridge between ends 2 and 3 of each set. This means that effectively, we have created one winding per set which is made up of two windings in series. So that leaves us with the following configuration:

Winding one:               U1 to U4

Winding two:               V1 to V4

Winding three:            W1 to W4

That means for us to connect this motor in Delta as per the manufacturer’s instructions for a 415V supply, we have to connect the following together:

U1 to W4

V1 to U4

W1 to V4

Thing to remember here is not to let the numbers throw you. Stick to the basic delta configuration and you will see it is quite easy. On a normal motor, the number 4’s would all be 2. That is the only difference once we have bridged the 2’s and 3’s

Great, we have figured out how to connect the motor and then we look at the terminal box to find the following: 12 ends and only 6 connector studs! Scary? Not really. Go back to your connection diagram and proceed as follows:

Connect U2 and U3 together on one stud, then V2 and V3 on the next stud and lastly, W2 and W3 on the third stud. We now have 6 wires left to go onto 3 studs. Look at the delta connection and follow it to give you the following:

U1 and W4 together on one stud and connect one phase from your contactor to this same stud

V1 and U4 together on the next stud with the next phase from your contactor to it

W1 and V4 on the last stud with the third phase from the contactor. Job done! Your motor is now connected in Delta and ready to be started

By the way, we did that and tested the motor. Running at 8.3A and quiet as it should be.

As usual, I hope you find this useful and remember to always work safe, test before you touch and do your installation test before you turn switches on!

Have a great week and for those who have not done it yet, check out the Manual for Electricians Volume 1 on: www.lulu.com/spotlight/SparkyHelp

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Remote Site Monitoring/Alarming

Had to do a job yesterday where we needed to set up remote site alarming for our client. In this case the client specified the hardware to be used and hence this article. When you do these installations, it is critical that you match the different types of hardware to your “back to base” unit.

The installation was set up with a number of pressure indicators but the design is such that we do not have voltage free contacts. So far this is not a big issue. The problem only occurred when the back to base unit was installed as this had its own power supply internally. In reality not a massive problem provided you are not on a very remote site when this happens.

Easy fix though, just had to wire in some relays very quickly to provide us with some voltage free contacts. This works but it is obviously not the most economical way of doing things. This does however lead me to the following: Mitsubishi Alpha controllers. These little units are incredibly powerful, easy to program and will not break the bank. Let’s take a look at how this would have worked in this application.

The outputs from the pressure devices would hook directly to the inputs of the controller. Write a very basic program to react on the signal, bring up a screen display to identify the alarm state and write this to the GSM block. You will need to add a GSM modem and the cable between the two units.

In the program you set up the message centre and the phone numbers you want to send the message to. Like I mentioned, these units are very easy to program. All the programming is done with LOGIC BLOCKS. If this is something that would interest you, I could set up some screen shots of a typical program with some explanations on it to help get you underway.

Keep in mind, these units can be used for controlling smaller machines, very powerful timers, counters etc. You could even set them up so that you can send a message to them from your phone to carry out an instruction. Just before anyone asks, No, I don’t sell them at all. I just love using them. I have set up so many programs with these and have not had one unit fail in almost 10 years since I started using them. Some of the sites where these units are installed would destroy many expensive PLC’s yet these little units just last

Let me know if this is something you would like to know more about. If there are enough requests I will set it up as a general Post for Members. Till next time, works safe and be proud of what you do. Make sure you retain the passion for what you do.

By the way, don’t forget to check out the Manual for Electricians Volume one available from www.lulu.com/spotlight/SparkyHelp

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