Know Your Enemy, Know Yourself

The installation of a system is not complete until it has been integrated with the client’s system

“If you know the enemy and know yourself, you need not fear the result of a hundred battles.”
If you know the circumstances and the respective strengths and weaknesses of both your enemies and your friends, you will never lose.

Sun Tzu

Kikusui’s products do not stand alone. Rather, they must work with the client device to which they are connected. My work therefore does not end with the installation of a system. Rather, a project is only complete when the system is tested connected to the object under test, and thereby integrated with the client’s equipment. In this job, having detailed information on the client’s circumstances (the client’s equipment and devices) in advance makes a big difference. Sun Tzu’s famous ’know your enemy, know yourself’ quote was about strategy in battle, but I believe it holds true for success in work as well. It is very important to do your homework.

While these days, I make a point of asking for all sorts of information when discussing specifications with a client. However, when I first started out in the job, I was more haphazard, or at least, I did not yet properly understand the nature of the job. This meant that there were several occasions when a system that had passed Kikusui’s shipping inspection would not conform with specification when installed on the client site.

Today’s story is my experience as delivered that became concerns when I was first time in charge of a system for clients.

My first assignment: a battery simulator

My first assignment was a battery simulation system that used a bespoke application to operate a Kikusui DC power supply and DC electronic load. The system allowed charging and discharging to be performed in the same way that it would be an actual rechargeable battery. (Figure 1)

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With everything ready to go, I transported the system to the client site and connected it to the client’s equipment to begin tests. While the tests started out smoothly, I suddenly noticed something troubling. The ammeter was displaying a lower current than the input current selected, the difference was being slightly greater than the ammeter’s accuracy.

While the tests found the system to be compliant with the client’s requirements, I did not know what was causing the disparity between the selected current and the current displayed on the meter. Needless to say, the system had performed fine when I tested it in the lab. With the customer’s permission, I disconnected our system from the customer’s and tested it again. I determined it to be functioning normally. The customer’s equipment was also determined to be functioning normally. In other words, the problem only manifested itself when our system was connected to the customer’s equipment.

As the disparity related to the current measurement, I next decided to look at the current sensing circuit, which worked by introducing a shunt resistor into the negative power line. It was in the process of comparing our system’s circuits with those of the client’s system that I realized what the problem was.

Grounding was the culprit

On close observation of the customer’s circuit diagram, I noticed that the customer’s equipment was grounded. The current sensing circuit in our system was also grounded. In electronics, ground (GND) denotes a reference potential. Despite what you might think in the case of electronic circuits, a device that is ’grounded’ is not necessarily earthed, or connected to the earth, although for reasons of safety and the prevention of signal noise, earthing is generally performed. It follows that grounding our system would have been a reasonable step to take, had the customer’s system and our system been independent of each other. However, the two systems needed to be connected, and when the two ground lines were connected to each other, a new circuit, separate from the circuit carrying the shunt current, was formed on the negative power line. That is, the charging current branched in two. The difference between the current displayed on the meter and the selected input current was due to the subtraction of this branch current. (Figure 2)

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Isolating the circuit

Now that I knew what was causing the problem, all that remained was to fix it. I isolated our system’s current sensing circuit so that it was no longer connected to ground. (Figure. 3)

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Once this modification had performed, the current displayed on the ammeter once again matched the selected current.

Nowadays, the isolation of a current detection circuit by using a current sensor would be a simple task. A system is only complete once when it is integrated with the client’s equipment. My experience with the battery simulator taught me the importance of properly understanding the customer’s setup before designing a system.

Aspiring engineers generally enjoy building things and can’t wait to ’get their hands dirty’. When you’re doing a project for fun, there’s nothing wrong with making up things as you go along. In fact, it’s actually more fun that way. When working for a client, however, it is important to prepare (research and design) before you start building anything. If you forego this step, it will come back to bite you, as it did me. I urge the young engineers reading this to take this to heart.

Please feel free to contact us with any questions or concerns.

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