Electronics > Metrology

Yet Another Hammon Divider (YAHD)

**rockstedy40**:

Hi everyone,

I’d like to get some feedback on this proposed design for a 10:1 and 100:1 Hammon divider. Nothing to special here, just using multiple resistors in parallel to keep the power dissipation to 1mW or less.

The resistors are Tyco YR1B’s which claim to be 0.1% with a TCR of 15 ppm. Not exactly Metrology quality, but good specs for $0.60 each. I’m hoping to use this for checking my Fluke 45, HP 3456A and various hand held meters. I realize that this is not up to the accuracy/stability required to really calibrate the HP, but I’m hoping it will give me a warm feeling that it’s good to 4 or 5 digits.

I’m also including a 1:1 divider to use as one half of a bridge to calibrate the Hammon Dividers.

I’m in the rotation for the Cal Kit and am hoping to use that to drive the divider to yield 1V and 0.1V outputs. I have the 10k and 100k resistors on order and plan on hand picking ones that allow for tweaking the last resistor to set the dividers.

Thanks all for your contribution to this great forum. This is a wealth of knowledge.

Bob[attachimg=1]

**GigaJoe**:

for fun you may try this :

for 1:10 , 2 major factors:

equal value of resistors

equal value of thermal coefficient, regardless of absolute value

so you may have a fun to buy a volume nonexpensive metal film (nonsmd) 1/4 W 50-100 ppm of desired value.

and about the same kind with value x10 approx.

pick 6 with the same TCR for both value ; as much as same , regardless of value.

next need to adjust all 6 to be the same resistance # ; that can be done by altering metal film, so resistance can be only increased

so we do in parallel - resistor one and another that x10 more, measure and pick one with highest resulting value, then altering by filer both original (if need) and x10 - to reach exact all 6 would the same. the better adjustment - the more precise divider would be

then construction depend on your desire of state of power dissipation , additional copper fins and oil bath or in brick of epoxy \ urethane , or oil filled sealed container. just remember that resistor coat need to be restored back ...

and before all measure you may do thermal stress by keep resistors for a few days at 110 - 130 Celsius

personally i use melf , and result some good one around less 0.1ppm TCR and 20 ppm dividing

an additional adjustment do even better when all finally assembled

**rockstedy40**:

GigaJoes, thanks for sharing your ideas. Not sure if I'm up to all this but let me at least try to understand.

1) Age/thermal stress all resistors for several days between 110 and 130 deg. C.

2) Measure TCR of each resistor and select 6 with the closest TCR's.

3) Using a file, adjust each resistor to match the one with the highest resistance. Now we have 6 resistors with close to the same TCR and resistance.

4) Not sure what you meant by the following:

"so we do in parallel - resistor one and another that x10 more, measure and pick one with highest resulting value, then altering by filer both original (if need) and x10 - to reach exact all 6 would the same. the better adjustment"

**Conrad Hoffman**:

Non-expensive metal films generally have a spiral pattern. No idea how you'd adjust them with a file or anything else. Just buy a bunch and select. Also, be sure to use hemostats or some kind of heatsink when you solder them, lest they change value by more than you might think!

**rockstedy40**:

"be sure to use hemostats or some kind of heatsink when you solder them," Good point! Thank you!!!!!! What a disaster to have soldered everything up only to find that all the resistors had drifted.

Navigation

[0] Message Index

[#] Next page

Go to full version