Wayne Kerr B224 Universal Bridge - UK Vintage Radio Repair and Restoration Discussion Forum

brian_mk · 28th Jun 2020, 10:23 am

I am looking for the user or service manual for the B224.

I've seen the previous thread.:-
https://www.vintage-radio.net/forum/...ad.php?t=40210

I've also looked at the manual for the older B221:-
https://www.pa3esy.nl/meetinstrument...accesories.pdf

I've used the bridge to measure capacitance several times in the past and it works very well.

However, I can't figure out how to measure inductance.
The spec indicates it can measure 1mH to 10kH to 0.1% and
100nH to 1mH to 0.3%.

If you look at the photo, there are three inductance ranges 1,2,3 marked 'uH' in blue on the top Range switch.
The decimal point indication for the 'C' term changes for each range.
For Range 1 it's after the most signifiant digit dial.
Range 2 it's the second digit, Range 3 it's the third digit.
That gives the following ranges:-
Range 1: 0 -> 9.999 uH
Range 2: 0 -> 99.99 uH
Range 3: 0 -> 999.9 uH

The first puzzle is how to measure inductance above 1mH?

I guess the way it's supposed to work for larger inductances is as suggested in the B221 manual:-
Set the 'C' term multiplier to '-1' and use the ranges 4 -> 10 (marked as uF, nF and pF).
Then use the formula L = 1/(w^2 * C).
If I try this for a 10mH inductor, I can get the bridge to balance on Range 4 (uF). The 'C' term reads 0.026 uF. The bridge frequency has been designed so that w^2 = 10^8 to make the calculation easy.
The calculation gives 0.38 which makes no sense.

If I try to meaure a small inductor e.g. 100uH using ranges 1,2 or 3 (for these ranges the 'C' multiplier appears to need setting to '1'), the results also make no sense. The bridge balances at the same 'C' term setting regardless of the range chosen and is the same even when the terminals are shorted together.

I don't know if the bridge is faulty or if I don't understand how to use it to measure inductance.

brian_mk · 28th Jun 2020, 10:49 am

Another thread refers to a different model - the B641.
It mentions that the B641 has the low impedance adapter built in:-

https://www.vintage-radio.net/forum/...d.php?t=133081

The external adapter is the Q221 referred to in the B221 manual.
Apparently this works by measuring equivalent series conductance and inductance rather than parallel conductance and capacitance.

I'm guessing that the B224 must also have the low impedance adapter built in and that this is used on ranges 1->3 for low inductance (< 1mH) and low resistance measurements.

brian_mk · 28th Jun 2020, 1:48 pm

I think I may have figured out part of the problem.
i.e. how to measure small inductors < 1mH.

After reading in more detail about the Q221 low impedance adaptor from the B221 manual I realised that the required connections to the component under test are not the same as when using the bridge stand-alone:-

Instead of connecting the unknown component in series between the center pins of the 'E' and 'I' BNC sockets, you use a four terminal arrangement with the unknown shunted to Neutral. One side of the unknown is connected to the two Neutrals (the 'E' and 'I' BNC outer contacts). The second side connects to both 'E' and 'I' BNC center pins.

I tried this arrangement to measure a 100uH inductor.
My vintage 1% Marconi TF2700 bridge measures this as 89.8uH with a DC resistance of 9.2 Ohms.
The B224 measures 86.2uH and 8.9 Ohms.
That's a difference in inductance measurment of around 4%.
According to the spec, the B224 should be within 0.3% in low impedance mode so it should be more accurate than the TF2700.

I still haven't figured out how to use the B224 to measure inductance above 1mH.

brian_mk · 28th Jun 2020, 4:53 pm

After more investigation, I think the mistake I made when measuring inductance >1mH is
not linking the two Neutrals together on the 'E' and 'I' BNC connectors.

As I suspected, for inductance measurements you have to set the 'C' multiplier to -1.
Once the bridge is balanced, you then have to calculate the inductance from the 'C' term.
The 'G' term gives the parallel conductance

To test the results I measured a coil in a ferrite pot core.
The Marconi TF2700 measures this as:-
L=64mH, R=2.2 Ohms.

The B244 balances with 'C' = 156.8 nF, 'G' = .007 mS

You then have to calculate L = 1/(10^8 * 156.8 x 10^-9) = 63.8mH

To calculate the equivalent series resitance you have to use the formula Rs = 1 / ( Gp * (1 + Q^2) )
Q is obtained from the ratio of 'C' / 'G' ignoring any decimal points. This gives 1568 / 7 = 224.
So Rs = 1 / ((0.007 * 10^-3) * (1+ 224^2)) = 2.8 Ohms.

The results agree fairly well - although the Marconi bridge is much easier to use.

I thought it a good idea to check the internal oscillator frequency as it's used when calculating inductance.
Assuming my frequency counter is accurate, it measured 1584.3 Hz compared to the nominal 1592Hz.

Does anyone else have experience using the B224 and can confirm I am using it correctly?

28th Jun 2020, 10:23 am	#1
brian_mk Tetrode Join Date: Mar 2015 Location: Milton Keynes, Buckinghamshire, UK. Posts: 91	Wayne Kerr B224 Universal Bridge I am looking for the user or service manual for the B224. I've seen the previous thread.:- https://www.vintage-radio.net/forum/...ad.php?t=40210 I've also looked at the manual for the older B221:- https://www.pa3esy.nl/meetinstrument...accesories.pdf I've used the bridge to measure capacitance several times in the past and it works very well. However, I can't figure out how to measure inductance. The spec indicates it can measure 1mH to 10kH to 0.1% and 100nH to 1mH to 0.3%. If you look at the photo, there are three inductance ranges 1,2,3 marked 'uH' in blue on the top Range switch. The decimal point indication for the 'C' term changes for each range. For Range 1 it's after the most signifiant digit dial. Range 2 it's the second digit, Range 3 it's the third digit. That gives the following ranges:- Range 1: 0 -> 9.999 uH Range 2: 0 -> 99.99 uH Range 3: 0 -> 999.9 uH The first puzzle is how to measure inductance above 1mH? I guess the way it's supposed to work for larger inductances is as suggested in the B221 manual:- Set the 'C' term multiplier to '-1' and use the ranges 4 -> 10 (marked as uF, nF and pF). Then use the formula L = 1/(w^2 * C). If I try this for a 10mH inductor, I can get the bridge to balance on Range 4 (uF). The 'C' term reads 0.026 uF. The bridge frequency has been designed so that w^2 = 10^8 to make the calculation easy. The calculation gives 0.38 which makes no sense. If I try to meaure a small inductor e.g. 100uH using ranges 1,2 or 3 (for these ranges the 'C' multiplier appears to need setting to '1'), the results also make no sense. The bridge balances at the same 'C' term setting regardless of the range chosen and is the same even when the terminals are shorted together. I don't know if the bridge is faulty or if I don't understand how to use it to measure inductance. Attached Thumbnails

28th Jun 2020, 10:49 am	#2
brian_mk Tetrode Join Date: Mar 2015 Location: Milton Keynes, Buckinghamshire, UK. Posts: 91	Re: Wayne Kerr B224 Universal Bridge Another thread refers to a different model - the B641. It mentions that the B641 has the low impedance adapter built in:- https://www.vintage-radio.net/forum/...d.php?t=133081 The external adapter is the Q221 referred to in the B221 manual. Apparently this works by measuring equivalent series conductance and inductance rather than parallel conductance and capacitance. I'm guessing that the B224 must also have the low impedance adapter built in and that this is used on ranges 1->3 for low inductance (< 1mH) and low resistance measurements.

28th Jun 2020, 1:48 pm	#3
brian_mk Tetrode Join Date: Mar 2015 Location: Milton Keynes, Buckinghamshire, UK. Posts: 91	Re: Wayne Kerr B224 Universal Bridge I think I may have figured out part of the problem. i.e. how to measure small inductors < 1mH. After reading in more detail about the Q221 low impedance adaptor from the B221 manual I realised that the required connections to the component under test are not the same as when using the bridge stand-alone:- Instead of connecting the unknown component in series between the center pins of the 'E' and 'I' BNC sockets, you use a four terminal arrangement with the unknown shunted to Neutral. One side of the unknown is connected to the two Neutrals (the 'E' and 'I' BNC outer contacts). The second side connects to both 'E' and 'I' BNC center pins. I tried this arrangement to measure a 100uH inductor. My vintage 1% Marconi TF2700 bridge measures this as 89.8uH with a DC resistance of 9.2 Ohms. The B224 measures 86.2uH and 8.9 Ohms. That's a difference in inductance measurment of around 4%. According to the spec, the B224 should be within 0.3% in low impedance mode so it should be more accurate than the TF2700. I still haven't figured out how to use the B224 to measure inductance above 1mH.

28th Jun 2020, 4:53 pm	#4
brian_mk Tetrode Join Date: Mar 2015 Location: Milton Keynes, Buckinghamshire, UK. Posts: 91	Re: Wayne Kerr B224 Universal Bridge After more investigation, I think the mistake I made when measuring inductance >1mH is not linking the two Neutrals together on the 'E' and 'I' BNC connectors. As I suspected, for inductance measurements you have to set the 'C' multiplier to -1. Once the bridge is balanced, you then have to calculate the inductance from the 'C' term. The 'G' term gives the parallel conductance To test the results I measured a coil in a ferrite pot core. The Marconi TF2700 measures this as:- L=64mH, R=2.2 Ohms. The B244 balances with 'C' = 156.8 nF, 'G' = .007 mS You then have to calculate L = 1/(10^8 * 156.8 x 10^-9) = 63.8mH To calculate the equivalent series resitance you have to use the formula Rs = 1 / ( Gp * (1 + Q^2) ) Q is obtained from the ratio of 'C' / 'G' ignoring any decimal points. This gives 1568 / 7 = 224. So Rs = 1 / ((0.007 * 10^-3) * (1+ 224^2)) = 2.8 Ohms. The results agree fairly well - although the Marconi bridge is much easier to use. I thought it a good idea to check the internal oscillator frequency as it's used when calculating inductance. Assuming my frequency counter is accurate, it measured 1584.3 Hz compared to the nominal 1592Hz. Does anyone else have experience using the B224 and can confirm I am using it correctly?