To: | kmwheeler@ualr.edu |
---|---|
Subject: | Re: The tachometer |
From: | "James J." <m1garand@speakeasy.net> |
Date: | Sat, 20 Mar 2004 18:45:54 -0500 |
Cc: | Barrie Robinson <barrier@bconnex.net>, mgb-v8@autox.team.net |
In-reply-to: | <10737a2106eb6c.106eb6c10737a2@ualr.edu> |
References: | <10737a2106eb6c.106eb6c10737a2@ualr.edu> |
Reply-to: | "James J." <m1garand@speakeasy.net> |
Sender: | owner-mgb-v8@autox.team.net |
User-agent: | Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax) |
To add to Keith's words, I'd use as high of a value as I can find (many
mega-ohms) since you want as little current passing through it as
possible. These types of pots are often called "trimmer pots" or
"cermet pots" because the resistive element is made from a plastic
called "cermet". You can find them in 20 or 30-turn units. Unlike
conventional "volume" pots that you find in radios, etc., these are
often long and rectangular with 3 little terminals coming out. We're
talking about something that looks like a 1" french-fry (or, ahem,
'freedom-fry'). RatShack might have these, but your best bet is Allied
or Mouser Electronics on-line. Now I don't know if there is a procedure for callibrating these, but if the Tach is just a voltmeter, then all you have to do is measure the resistance across the entire potentiometer, and then adjust the tap until you read exactly 1/2 that value. A 20-turn pot gives you alot of resolution to get to exactly the right value. This will give you exactly 1/2 the input voltage, but if the pulse-to-volt converter is off, this will also be off. If you have a DMM that has a pulse-counter (or a timing-gun with a tach) you can tweak the potentiometer to compensate for any linear errors in the p-to-v converter. Best of luck!!! JJJ kmwheeler@ualr.edu wrote: Barrie, /// /// mgb-v8@autox.team.net mailing list /// Send admin requests to majordomo@autox.team.net /// Send list postings to mgb-v8@autox.team.net /// Edit your replies! If they include this trailer, they will NOT be sent. /// |
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