1. Avometer Model 40 Manual
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The Universal AVOmeter model 8 was the most ubiquitous multimeter in the AVO range which started life. There is NO VAT payable on manuals. Wrist Strap & Shoe.

Repairing a burnt shunt for an AVO 8 Mk 1 and Mk 2 is extremely simple. The Avometer design was specifically such that an engineer could repair a burnt shunt, and as a result, both meters have a pair of long circuit boards, where the bottom one consists of the shunt resistor windings. A universal meter usually has many shunts that switch into the circuit to provide different ranges. If you are a Brit, the word 'shunt' that is eventually spoken in connection to meters may confuse you. It was more in use in America to represent a parallel railway track, or a sidetrack. However the principle is the same, and instead a parallel resistance across the meter coil provides an additional path for the electrons to follow. If the parallel resistance is the same as the meter coil resistance, then double the current is required to cause a full-scale deflection.

There are eleven shunts on this board beginning with a 6200 Ω resistance, made of two fixed resistors in series. The rest of the shunts are made of Eureka wire, also known as constantan wire. If memory serves, from my O’ Level Chemistry days, this copper-nickel alloy is temperature stable and you can solder on it, making it useful for building precision resistors. Manganin is a better alternative, because it is more superior where resistance stability is concerned, but it is more expensive. That is why many high-end meters use manganin shunts instead.

  1. AVO Avometer 7 - Analog multimeter - Service and User Manual -- Free Service Manuals.
  2. Universal AvoMeter Model 40 Equipment AVO Ltd.; London, build 1939??, 8 pictures, 1 schematics, Great Britain, tubes, semiconductors, Service- or Lab.
  3. 0 admiralty pattern 4. The Admiralty Pattern 4. A is one of two Avometers which I know to have been supplied to the Admiralty during the 1.
  4. The AVO 8 Mk 2, also known as AvoMeter 8 Mk 2 is a Universal multimeter. And some of the older AVOs such as the Model 40 and earlier AVO 7s. Manual, AVO 8 User.

The resistance must remain stable in shunt wires; otherwise, it can destroy the calibration and accuracy. When buying resistance wires, there are three main properties to consider. They have a thickness determined by Standard Wire Gauge (SWG) number, a resistance value given in ohms-per-metre, and can be in enamelled or bare wire form. The enamelled wire has an insulation coating and therefore ideal to make a resistor, unfortunately, it is difficult to find a cheap wire in this category.

The 1200 Ω, 300 Ω, and 450 Ω shunts require 46 SWG wire, however, the service instructions do not state the length of wire required, or the ohms-per-metre parameter, and instead mentions the number of turns. Perhaps back then, the choice was limited and was a well-known standard, however today there is a wide choice of gauges, composition, and specifications.

The ohms-per-metre parameter is critical because if it is too small, then you will need to wind large lengths of coil to build the larger value shunts, and making the coils too large is not desirable because it would introduce inductance into the circuit. The gauge of the wire is also important because it determines the amount of current the wire is capable of carrying. /alphacam-7-crack-serial-numbers/. In the Model 8, they are using 22 SWG, 40 SWG, 46 SWG (0.0610 mm), 40 SWG, and 44 SWG thicknesses for the various current ranges.

Unfortunately, in the Avometer I bought on eBay, two of the shunts were completely burnt, and the remaining coils that seemed fine were open as well. This meant removing all the damaged shunts and rewinding new ones. In addition, the bottom board was broken and required joining.

Looking on the internet for replacement constantan wire, I realised that UK suppliers were very expensive making the repair uneconomical. However, I was determined to get this meter working, and decided to look on eBay.


The only gauge that came close to my requirements, that I could afford, was a 44 AWG (0.0500 mm) wire, which is very thin.

'0.05mm 44AWG 247Ω/m 75Ω/ft, CuNi44/Isotan/Constantan Resistance Wire kanthal, 7m'

It had a resistance rating 247 Ω/m and they were selling a 7 m length for less than two pounds, which was just affordable for my pocket, hence I decided to get this wire and use it to make the replacement shunt resistors.

Given the resistance rating of the wire to be 246 ohms-per-metre, I calculated the length of wires required to make the replacement shunts.

ShuntResistance (Ω)Gauge / Dia (mm)Wire Length (m)
298044 SWG (0.0813) 3.980
36440 SWG (0.1219) 0.260
41200 46 SWG (0.0610) 4.878
530046 SWG (0.0610)1.219
645046 SWG (0.0610)1.829
74240 SWG (0.1219) 0.171

Therefore, a total of approximately 12 metres of wire would be required. I decided to use the same wire for all the shunts because they were for low current ranges and therefore had negligible impact to the operation. Looking at the extremes, the 1200 Ω shunt requires 4.878 m of wire; however, the smaller 42-Ω shunt requires only 17.1 cm length of wire. Winding 4.878 m of wire is quite a lot so I decided to use a high precision resistor there.

Higher secondary physics book bangladesh free. If you had some extra money, then you could use a lower value (ohms-per-meter) for the 42-Ω shunt, which would allow you to work with a longer wire. However, on my meagre blogger budget, beggars cannot be choosers as they say.

This Article Continues..

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