Video: CA 6630

Video transcript

What the internal resistance of a battery tells you, and how the CA 6630 measures it, together with the voltage, in a single reading. A cell starts to fail long before a battery loses noticeable capacity, and its voltage on float hardly changes. What does change is its internal resistance. Measured regularly, it points at the weak cell before the battery lets you down. The CA 6630 measures the internal resistance by the four-wire method, from 40 milliohms up to 40 ohms full scale,

and at the same time the open-circuit voltage, on a 4 or a 40 volt range. Both readings appear together on the display. Each probe carries two contacts. One pair injects a small alternating current at one kilohertz; the other pair measures the voltage right at the terminals. Because the voltage is taken at the battery and not at the instrument, the resistance of the leads drops out of the result. The double display shows resistance above and voltage below.

Under it, 3 LEDs give the verdict of the comparator. Then the arrows and SET, the range keys, HOLD, and memory and read. And the label on top is a reminder of the two erase shortcuts. It comes in a rigid case, with 2 1 metre measuring leads that end in retractable contact tips, the PC software, the cable to connect the instrument to the computer, and the manual. The red lead goes into the positive input and the black lead into the negative. Switch the instrument on. Then the red tip on the positive terminal of the battery,

and the black tip on the negative. The reading is immediate. Before the first reading, compensate the leads: short the two tips together and press REL. The display goes to zero, and from then on the leads are subtracted. Then choose the ranges, touch the terminals, and read resistance and voltage together. It measures batteries, not the network. Never more than 50 volts DC on the inputs, and never an alternating voltage.

And after a high-voltage battery, short the leads before moving to a low-voltage one, to remove any charge they have picked up. The comparator is what makes it fast. Each reference holds a low and a high resistance limit and a voltage limit. The reading is compared with it, and one LED lights: pass, warning, or fail, with a beep if you want one. Up to 99 references can be stored, one per battery type. Hold SET for two seconds, choose the reference number,

and enter the low and high resistance limits and the voltage limit. From then on, SET switches the comparison on or off. Each reading can be stored with one key: up to 999. Or the instrument can log on its own, at an interval from one to 255 seconds, with 9600 samples. Logged data are read on the PC. The PC software, supplied with the instrument, downloads the stored results through the communication interface, exports them,

plots the data-logger values as graphs, and keeps every result on the computer, so each cell can be followed from one maintenance round to the next. It runs on 6 AA batteries, for about 7 hours of use, and switches itself off after 30 minutes without a key press. If it is stored for more than two months, take the batteries out. Clean it with a soft, damp cloth, never with solvents. It is used on the stationary batteries of uninterruptible power supplies, telephone exchanges and security installations, to find weak cells before

capacity falls, and to follow each cell from one maintenance round to the next. Battery maintenance, from Amperis.