Hi,
I am new to the forum, and have a beginners level knowledge of circuit design.
System Information
I have a system with a mains powered 240VAC control unit.
The control unit has a 240VAC and 5VDC side, with galvanic isolation beween the two, possibly achieved by a transformer, followed by some form of rectifier for the AC - DC conversion, I don't know the internal design.
I have a flow meter wired to the controller's 'Low voltage' (LV) side, with 3 wires as per the attached image, labelled as follows.
1. A +5DC supply
2. A GND return
3. A pulse frequency return signal
[?]I don't exactly understand this, is it constant current, variable frequency?
One can measure the frequency rate of no.3 in Hz, and convert that to a flow rate using a table.
The Problem
In a 0L/min no flow case, the flowmeter outputs (in error) 50Hz, and the controller thinks there is a ~4L/min flow and takes action.
What I've tried
(I) Bonding pipework: Makes no difference
(II) Bring the unit to another country, with a 'cleaner' power supply: Makes no difference
(III) Hard wiring the controller GND connection to an external Earth terminal also: Issue fixed.
I have been told by the controller manufacturer that this is very 'dangerous' and should not be done.
[?] How dangerous is it? If a user touches a live +5VDC wire on the LV side with a earth in place current will flow.
The - or 0VDC connection on the controller is actually at a measurable 45mV relative to Earth. Does that mean the LV side is floating?
[?] Would a component that needs a 5VDC supply react give errors due to this potential above Earth.
[?] Does LV GND as specified by the flowmeter manufacturer mean it should be at 0V relative to Earth, or would 5VDC supply in a floating system be ok.
Thank you in advance for your help. If you need more info please comment.
I am new to the forum, and have a beginners level knowledge of circuit design.
System Information
I have a system with a mains powered 240VAC control unit.
The control unit has a 240VAC and 5VDC side, with galvanic isolation beween the two, possibly achieved by a transformer, followed by some form of rectifier for the AC - DC conversion, I don't know the internal design.
I have a flow meter wired to the controller's 'Low voltage' (LV) side, with 3 wires as per the attached image, labelled as follows.
1. A +5DC supply
2. A GND return
3. A pulse frequency return signal
[?]I don't exactly understand this, is it constant current, variable frequency?
One can measure the frequency rate of no.3 in Hz, and convert that to a flow rate using a table.
The Problem
In a 0L/min no flow case, the flowmeter outputs (in error) 50Hz, and the controller thinks there is a ~4L/min flow and takes action.
What I've tried
(I) Bonding pipework: Makes no difference
(II) Bring the unit to another country, with a 'cleaner' power supply: Makes no difference
(III) Hard wiring the controller GND connection to an external Earth terminal also: Issue fixed.
I have been told by the controller manufacturer that this is very 'dangerous' and should not be done.
[?] How dangerous is it? If a user touches a live +5VDC wire on the LV side with a earth in place current will flow.
The - or 0VDC connection on the controller is actually at a measurable 45mV relative to Earth. Does that mean the LV side is floating?
[?] Would a component that needs a 5VDC supply react give errors due to this potential above Earth.
[?] Does LV GND as specified by the flowmeter manufacturer mean it should be at 0V relative to Earth, or would 5VDC supply in a floating system be ok.
Thank you in advance for your help. If you need more info please comment.
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