![]() ![]() ![]() Now put your reference resistors between the wires, activate the meter and set the trimmpots as described before, i.e. Disconnect the thin wire you previously attached to the free leg of the LDR and attach it to the corner pad on the meter’s PCB, where the LDR should be connected. I have put a lot of notes into the XLS, look for the red cornered fields and read them, they might explain what hasn’t been made clear here.If the data seems OK, take few fixed resistors (or precision potentiometers), read from the column “R computed” to what reading do their values (measured values!) correspond, and note it down.Now install the diode into your meter, reattach the battery wire, but DON’T re-install the LDR yet. Because of this, in most cases it is possible to readjust the meter for 1.55V silver oxide cells with no further hardware modifications. As CdS cells are not made to very tight tolerances CdS based meters have to provide for a relatively wide adjustment range. For details on such meter design see my article (although the relevant PDF isn’t finished yet, the part covering mercury cell based meters is ready).Being a purely passive, resistive, linear circuit it has no principal problem with a slightly higher battery voltage, besides showing wrong exposure values of course. Light is detected using a CdS (Cadmium Sulphide) LDR (light dependent resistor) that directly influences amount of current allowed into the galvanometer. ![]() There are only resistors and the galvanometer in it, no diodes, no transistors, no fancy electronic circuitry. Since the amount of silver in these button batteries is tiny, the manufacturing cost difference isn’t really relevant to the sale price, but it shows why the mercury was used in the first place – cents sum up to dollars fast.The Gossen Lunasix is a purely passive circuit, i.e. Silver oxide cells have equally stable voltage output and are based on the same principle, as mercury batteries, the main difference being use of silver in place of mercury, which makes these batteries more expensive to manufacture. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |