Hall Effect sensor "sticks" on

[MikeremlaP]

Built a tachometer transducer using a Hall Effect sensor. Has worked well many
years but now is failing. Have discovered that the Hall Effect sensor tends to
"stick" on, even when no magnetic field around, as long as power is on.

On the assumption it's not the hysteresis circuit inside the device, I tried
degaussing the sensor. No success so far. Anyone ever heard of this happening
before and anyone got a fix? Could make a new transducer with a new part, but
the whole thing is potted in epoxy. If there's an easy fix, would like to try
that first.

Thanks,

Mike Palmer <><
Excellence in Ergonomics

 

[James Meyer]

On 29 Jan 2005 05:10:43 GMT, mikeremlap@aol.comnet.org (MikeremlaP) wroth:

Built a tachometer transducer using a Hall Effect sensor. Has worked well many
years but now is failing. Have discovered that the Hall Effect sensor tends to
"stick" on, even when no magnetic field around, as long as power is on.

On the assumption it's not the hysteresis circuit inside the device, I tried
degaussing the sensor. No success so far. Anyone ever heard of this happening
before and anyone got a fix? Could make a new transducer with a new part, but
the whole thing is potted in epoxy. If there's an easy fix, would like to try
that first.

There is no easy fix. Hall sensors are a cross between electronic ICs
and microminiature mechanical devices. The whole thing is very sensitive to
heat and physical stress on the package. I suspect that the sensor has degraded
and is now effectively "dead".

Potting compounds, especially simple epoxys meant for adhesive purposes,
can generate enormous strain on IC packages especially when combined with heat
cycles.

When (not if) you rebuild the assembly, take care to either use potting
compounds meant expressly for sensitive electronics or use a flexible buffer
coat over the hall sensor before potting the entire assembly.

Jim

 

[Jamie]

MikeremlaP wrote:

Built a tachometer transducer using a Hall Effect sensor. Has worked well many
years but now is failing. Have discovered that the Hall Effect sensor tends to
"stick" on, even when no magnetic field around, as long as power is on.

On the assumption it's not the hysteresis circuit inside the device, I tried
degaussing the sensor. No success so far. Anyone ever heard of this happening
before and anyone got a fix? Could make a new transducer with a new part, but
the whole thing is potted in epoxy. If there's an easy fix, would like to try
that first.

Thanks,

Mike Palmer
Excellence in Ergonomics

Yup, i have seen it happen.,

replace the component.

 

[whiskerstherat]

Jamie wrote:

MikeremlaP wrote:

Built a tachometer transducer using a Hall Effect sensor. Has worked
well many
years but now is failing. Have discovered that the Hall Effect sensor
tends to
"stick" on, even when no magnetic field around, as long as power is on.

On the assumption it's not the hysteresis circuit inside the device, I
tried
degaussing the sensor. No success so far. Anyone ever heard of this
happening
before and anyone got a fix? Could make a new transducer with a new
part, but
the whole thing is potted in epoxy. If there's an easy fix, would
like to try
that first.

Thanks,

Mike Palmer
Excellence in Ergonomics

Yup, i have seen it happen.,
replace the component.


You may want to double check the type of sensor you have. Some are made

to latch on, and be turned off with the other poll of a magnet.

Also, you may check to be sure that you do not have excessive current
through the device. Sometimes, this can cause a device to latch up.

You may also check to be sure that the strength of the magnet is not
to powerful to damage the sensor. Some mfg. do not like to see
excessive magnetic fields.

The third thing may try to place a 0.1 uF cap across the power leads as
close to the sensor as possible. Sometimes, a sensor will misbehave
without this.

Whiskerstherat