GA-52CX Calibration??

[bklein]

Anyone have an understanding of the calibration procedure for the GA-52CX?

[Altra]

What problem are you having or why do you want to calibrate it? One of the trimmers is for tx frequency. Another trimmer, I believe sets the audio null/threshold for no signal. The third is connected to the transmit circuit not sure if it adjust output level or some kind of distortion adjust? I have not had time to reverse my pcb.

The manual states the idle audio frequency is 40Hz

[bklein]

I have restored a few of these and can’t tell if calibration is necessary or not - I don’t know what a good test for it would be. I don’t notice a difference between units just sensing random ferrous targets around my home.

[Altra]

It's really hard to test any kind of magnetometers around buildings. Probably the best test would be some area away from people and trash. Using standard iron items for test targets. Reading some of their patents, most of the calibration takes place at the factory with careful alignment of the two sensors. I have not tried to pull the sensor assembly out of the tube yet!

[Carl-NC]

I would use a bar magnet to measure sensitivity, I personally use a cow magnet. Flip it end-over-end and see how far away it can be detected. Compare to a known good unit.

Most magnetometers (and I assume GA-52CX) are dual-sensor gradiometers. There is probably a calibration method for aligning the sensors which might be mechanical, circuit-based (e.g. trimmer), or software-based. If you are away from any iron metal and you rotate/roll/flip the mag in free space it should not respond to Earth field. If it does, then the sensors need alignment calibration. If it does not, and sensitivity is consistent with a known good unit, then you shouldn't need to do anything.

[Daves]

I would use a bar magnet to measure sensitivity, I personally use a cow magnet. Flip it end-over-end and see how far away it can be detected. Compare to a known good unit.

Most magnetometers (and I assume GA-52CX) are dual-sensor gradiometers. There is probably a calibration method for aligning the sensors which might be mechanical, circuit-based (e.g. trimmer), or software-based. If you are away from any iron metal and you rotate/roll/flip the mag in free space it should not respond to Earth field. If it does, then the sensors need alignment calibration. If it does not, and sensitivity is consistent with a known good unit, then you shouldn't need to do anything.

Hi Carl,
what is the "alignment calibration" how do you define and explain this? Like ground balance in detectors?, I would appreciate it if you could explain it.

[Carl-NC]

I can't explain it because it depends on the mag design. But, ultimately, you want the mag to have no response when it is rotated in free space. A little like GB, kinda sorta.

[Orbit]

When it rotates in free space? If you adjust the sensors when the pipe is horizontal with that and the pipe is in a position for example north south! Any rotation in other directions will cause a decrease or increase in the frequency output on the sensors! Specifically, I mean fgm 3.The same happens with the flc 100 or a copy of the ems 100 or some sensors that I bought from Great Britain and are used in the gpa 1000. However, depending on the change, it can be done in hardware or software to do something like geb balance, I specifically did that on the hardware, for example, the input to the processor expects 500mv, that hardware accessory always sets the input to the expected 500mv when I press the button. From 500mv it can go to 0v or up to 5v plus when it finds anomalies. Gpa 1000 does it softer. I did that let's call it a geb balance with flc 100 sensors that give a dc voltage at the output. It seems to me that I got the best performance and the most stable operation when the sensors are placed horizontally 50 cm apart.

[Orbit]

If I forgot to write, as I said, the processor, for example, expects 500mv, but the measurement in the minus starts at 400mv and in the plus of 600mv, that's what I called the neutral field! Because there is a slight drift condition due to component voltages or external disturbances. That neutral field affects a slightly lower sensitivity if the measurement starts immediately, the sensitivity is higher with the possibility of giving false readings due to the above.

[Orbit]

On the Expore 5000 or 3000, the sensor outputs enter the precise rial to rial, one on the inverting input, one on, not inverting, as we lower the sensors towards the ground, if there is no metal in that place, a kind of ground balance is performed, one sensor pulls in the plus, the other in the minus, and we have at the output of the amplifiers, the voltage is zero, when the sensors pass over the metal, the sensors react depending on which side the object is on, and the voltage goes to plus or minus as soon as we cross that field, thanks to that accessory, the sensors perform some kind of automatic calibration!

[Carl-NC]

When it rotates in free space? If you adjust the sensors when the pipe is horizontal with that and the pipe is in a position for example north south! Any rotation in other directions will cause a decrease or increase in the frequency output on the sensors!

That is true for a simple 2-sensor design. I assume most commercial mags (for utilities, like the GA-52CX) include 3-axis sensors; the Z-axis for main detection, and X & Y axes for Earth field calibration. When you have sensors on all 3 axes you can calibrate it to rotate freely in Earth field with no response.

[Daves]

I can't explain it because it depends on the mag design. But, ultimately, you want the mag to have no response when it is rotated in free space. A little like GB, kinda sorta.

DC data comes from the sensors, what is the alignment that will be done on the north-south or a different axis? I couldn't fully understand this. (If we are talking about FLC-100)
We could do this at least with a target in the metal detector. What will we convert the DC data to and then align?
I couldn't fully understand the alignment procedure.
Orbit

[Carl-NC]

With a single axis gradiometer, you want both sensors exactly aligned axially so that when you rotate the mag on that axis there is no response. If one of the sensors is slightly angled, then there will be an increasing/decreasing response as you rotate the mag.

[Daves]

With a single axis gradiometer, you want both sensors exactly aligned axially so that when you rotate the mag on that axis there is no response. If one of the sensors is slightly angled, then there will be an increasing/decreasing response as you rotate the mag.

So, what is meant by alignment? Is it to align the sensor so that it points perpendicular to the ground? Or is alignment = a software procedure?

[Orbit]

So, what is meant by alignment? Is it to align the sensor so that it points perpendicular to the ground? Or is alignment = a software procedure?

I personally line them up vertically down towards the ground.!?