<p>As always cost will be a factor.  I found the M4 sensors to be be just not good enough, they have to be too close, and eventually it's going to catch on your print and damage sensor mounting and/or the hot-end assembly.</p>

<p>The 8mm range sensors seem like a good distance, but you'll need to decide between a wider, heavier but cheaper model or the think, lighter more expensive model.</p>

<p>If your goal is to optimise for speed, go the lighter version.</p>

<p>In terms of sensing accuracy, if your layer height is typically 0.2mm then I don't think there's much point paying for more accuracy.</p>

CC BY-SA 3.0
2018-03-24T08:54:56.233Z
2018-03-24T08:54:56.233Z
Matt
<p>Duet3D has a very nice <a href="https://duet3d.dozuki.com/Wiki/Choosing_a_Z_probe" rel="nofollow noreferrer">overview</a>. It totally depends on your demands. e.g., accuracy, different build surfaces, tolerance. Personly I realy like the <a href="https://www.precisionpiezo.co.uk/shop" rel="nofollow noreferrer">piezo</a>. It actually uses your nozzle to 'touch' the bed. So 0 height is absoluty 0. This eliminates the need for Z-offset.</p>

CC BY-SA 4.0
2019-05-15T21:05:59.613Z
You still need to set up z-offset for the piezo.
https://docs.wixstatic.com/ugd/e08222_ae707c20a0cf418b8393b44368370576.pdf

_Whilst there is no x or y probe offset as the probe is the nozzle, and this is one of the most advantageous features of this system, there does need to be a slight Z offset as the assembly bends slightly on probing._
Makotosan
CC BY-SA 4.0
2018-07-10T15:06:54.530Z
2018-07-10T15:12:04.607Z
2018-07-10T15:12:04.607Z
Shwans
<p>Tomas Sanladerer has produced a nice video on this topic: <a href="https://www.youtube.com/watch?v=il9bNWn66BY" rel="nofollow noreferrer">https://www.youtube.com/watch?v=il9bNWn66BY</a></p>

<p>@ 7:31 you see an overview of the precision of various sensors, including the ones you mention. It appears that the M12-4 and M18-8 sensors are more accurate than the M8-8.</p>

CC BY-SA 3.0
2018-03-21T13:22:39.303Z
I saw it, that is what made me more confused and i asked this question.
Jose Ben
CC BY-SA 3.0
2018-03-21T14:02:28.583Z
It depends on your surface. Inductive works for Aluminium heat beds, but not when covered with glass. Capacitive sensors are inaccurate and should be avoided. The touch sensor types work with all surfaces.
0scar
CC BY-SA 3.0
2018-03-21T15:34:56.103Z
5v or 6v-36v  which one should I use???
Jose Ben
CC BY-SA 3.0
2018-03-21T18:56:54.007Z
I'm using the LJ18A3 - 8-Z / BX DC6-36V 8 mm Inductive Proximity Sensor NPN @ 12V using an OptoCoupler module.
0scar
CC BY-SA 3.0
2018-03-21T19:57:24.133Z
What is the surface of your heat bed? Glass or aluminium with tape?
0scar
CC BY-SA 3.0
2018-03-22T07:31:43.090Z
Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/74906/discussion-between-jose-ben-and-0scar).
Jose Ben
CC BY-SA 3.0
2018-03-22T07:34:37.387Z
My bed is mk3 Aluminium. What is an optocoupler???Why do we need it???Can you share the wiring diagram?
Jose Ben
CC BY-SA 4.0
2018-07-10T16:07:34.217Z
@JoseBen Actually, that recently became a question of its own: https://3dprinting.stackexchange.com/questions/6358/inductive-sensor-in-24v-machine
Trish
CC BY-SA 3.0
2018-03-21T11:52:07.983Z
2018-03-21T11:52:07.983Z
0scar
<p>I am building a <a href="https://andypi.co.uk/2017/09/17/dolly-build-notes-prusa-i3-mk2-clone-3d-printer/" rel="nofollow noreferrer">dolly</a> and I am confused as to which proximity sensor to use. </p>

<p>Should I go for M8 or M12 and 5&nbsp;V or 6-36&nbsp;V? </p>

<p>What should be the best detecting distance? Should it be 2/4/8&nbsp;mm. Which one should I select?</p>

CC BY-SA 3.0
2018-03-22T02:29:52.967Z
I'm using  LJ18A3 - 8-Z / BX DC6-36V to 12V works great!
Fernando Baltazar
<prusa-i3><diy-3d-printer><z-axis><z-probe>
Which proximity sensor to use?
Jose Ben
# Which proximity sensor to use?

(Asked by: username_0 on 2018-03-21)

I am building a [dolly](https://andypi.co.uk/2017/09/17/dolly-build-notes-prusa-i3-mk2-clone-3d-printer/) and I am confused as to which proximity sensor to use.

Should I go for M8 or M12 and 5 V or 6-36 V?

What should be the best detecting distance? Should it be 2/4/8 mm. Which one should I select?

**Tags:** prusa-i3, diy-3d-printer, z-axis, z-probe
> **Comments:**
> **username_1**: I'm using  LJ18A3 - 8-Z / BX DC6-36V to 12V works great!  

---

## 3 answers

### Answer by username_5 on 2018-03-21. Score: 2 | Accepted answer

Tomas Sanladerer has produced a nice video on this topic: <https://www.youtube.com/watch?v=il9bNWn66BY>

@ 7:31 you see an overview of the precision of various sensors, including the ones you mention. It appears that the M12-4 and M18-8 sensors are more accurate than the M8-8.

> **Comments:**
> **username_0**: I saw it, that is what made me more confused and i asked this question.  
> **username_5**: It depends on your surface. Inductive works for Aluminium heat beds, but not when covered with glass. Capacitive sensors are inaccurate and should be avoided. The touch sensor types work with all surfaces.  
> **username_0**: 5v or 6v-36v  which one should I use???  
> **username_5**: I'm using the LJ18A3 - 8-Z / BX DC6-36V 8 mm Inductive Proximity Sensor NPN @ 12V using an OptoCoupler module.  
> **username_5**: What is the surface of your heat bed? Glass or aluminium with tape?  
> **username_0**: Let us [continue this discussion in chat](https://chat.stackexchange.com/rooms/74906/discussion-between-jose-ben-and-0scar).  
> **username_0**: My bed is mk3 Aluminium. What is an optocoupler???Why do we need it???Can you share the wiring diagram?  
> **username_6**: @JoseBen Actually, that recently became a question of its own: https://3dprinting.stackexchange.com/questions/6358/inductive-sensor-in-24v-machine  

---

### Answer by username_2 on 2018-03-24. Score: 1

As always cost will be a factor. I found the M4 sensors to be be just not good enough, they have to be too close, and eventually it's going to catch on your print and damage sensor mounting and/or the hot-end assembly.

The 8mm range sensors seem like a good distance, but you'll need to decide between a wider, heavier but cheaper model or the think, lighter more expensive model.

If your goal is to optimise for speed, go the lighter version.

In terms of sensing accuracy, if your layer height is typically 0.2mm then I don't think there's much point paying for more accuracy.


---

### Answer by username_3 on 2018-07-10. Score: 1

Duet3D has a very nice [overview](https://duet3d.dozuki.com/Wiki/Choosing_a_Z_probe). It totally depends on your demands. e.g., accuracy, different build surfaces, tolerance. Personly I realy like the [piezo](https://www.precisionpiezo.co.uk/shop). It actually uses your nozzle to 'touch' the bed. So 0 height is absoluty 0. This eliminates the need for Z-offset.

> **Comments:**
> **username_4**: You still need to set up z-offset for the piezo. https://docs.wixstatic.com/ugd/e08222_ae707c20a0cf418b8393b44368370576.pdf  _Whilst there is no x or y probe offset as the probe is the nozzle, and this is one of the most advantageous features of this system, there does need to be a slight Z offset as the assembly bends slightly on probing._  

---

