Testing of CALMU at AECo meter testing laboratory
At AECo (Ahmedabad Electricity Company - presently Torrent Power) we had a practice of testing and calibrating each meter received from our supplier. In those days meters were tested using a RSS meter (Rotary Sub Standard) where the disc-rotation of the meter under test and the rotation observed on the RSS were compared. The error was computed considering meter constant (revolution per kWh) of RSS and the meter under test. RSS had to be imported and was an expensive instrument with high accuracy.
As required by the metering standards, we were purchasing single-phase and three-phase meters of class 2 accuracy and the meters for HT customers were of accuracy class 1.
The first lot of CALMU meters that we bought were used for a different purpose, hence we did not test them and installed them at customer HT panels. I have narrated this in another story, “First order from AECo and how AECo used CALMU”.
We were so very enthusiastic about installing CALMU meters received under our first and second order, and deriving the benefits from them, that we never thought of testing them. By the time we received our third order, we thought of testing them. To our surprise, each and every meter failed! I became very nervous since by then I had been thinking of using them for billing. Further, what about the purchase of meters under our first and second order? If someone tells my MD or ED that I have waived the inspection at manufacturer laboratory, accepted the meters and passed the bills without testing the meters, how will I be able to defend myself and save face? Will I be blamed?
I could not sleep that night. Next day I went to the telephone / telegraph office in the Bhadra area (I wanted to keep the conversation confidential) and booked a trunk call to Babel sb. I narrated the test results of CALMU and asked him to come down immediately to witness the tests. I told him my situation and said that if he delayed, someone may blame me. To my surprise, the next day in the morning at 08:00 am Sanjay sb and Babel sb were both at my laboratory in Ahmedabad.
We tested the CALMU and saw the results obtained. Both of them were surprised to see the odd results; another two CALMU were tested – same results. The results obtained that day were compared with the results obtained a few days before; we could not derive any conclusion. Sitting in the cabin scratching heads, we could not find any reason. Many cups of tea were drunk, the tin of ‘Pan Parag ’ was getting empty.
Suddenly Sanjay Saab went out of the cabin, walked fast to the testing bench, checked the wiring, the CALMU and the RSS, and came hurriedly back to the cabin cheerfully saying ‘Eureka, eureka!’
He asked me if we had another better RSS. I said this one is the only one, there is no better RSS.
Sanjay Saab explained, the RSS is of Class 0.5 and our CALMU is also 0.5 (in fact it was Class 0.2). To test the CALMU, you need to use a Class 0.2 RSS. The standard comparator instrument must be of one-step better accuracy. He also suggested testing at Udaipur for better satisfaction with witnesses from AECo. I immediately deputed my junior and asked him to travel by night to Udaipur with the three CALMU meters which we had tested, and asked him to witness the test and inform me of the results by phone.
The next day I remained confined to my cabin, remaining in touch with my junior on phone, asking him about the progress. On hearing from him by the evening that the meters were accurate I felt relaxed and guilt free.