long distance transfer of analogue signal

[TF and the wire]

I have to pick up an analogue current 0-20mA from a transducer that converts steam pressure to current, and transfer it over 200 metres to a boiler house, and then convert it back to either 0-10v or 0-20mA or even 4-20mA (trying to find out exactly what they want).

Whats the best way to do it.

 

[Notsosmart]

The distance iisn't an issue but you need to get the customer to define exactly want they want. What kind of input module is to be used, do you need to supply 24V to the pressure switch, if it is 0-20mA ~ 0-10V is easy to convert (500Ohm resistor across the incoming terminal) Otherwise us a signal conditioner etc.

 

[netblindpaul]

One thought,
A-D/D-A? Depends on how accurate you need it?

 

[Deleted member 15225]

Pressure sensors are usually 4-20mA. Does this sensor also come with a transmitter? They usually do. If it's RS485 just run the serial output from this to the boilerhouse.

 

[TF and the wire]

Just a transducer that gives 0mA for 0bar and 20mA for 16 Bar. The boiler people are still fannying around so i just intend getting a 0-20mA signal and let them sort out what they want to do with it.

I don't want it to affect the original measurement displayed on the machine desk. So intend using a signal conditioner.

The distance is more like 300m. Is that a problem.

Anyone give me the finer detail.

 

[NoSparks]

I've just been reading the spec for an AD converter which may be usefull:

Analog transmitter output, 16-bit, scalable and isolated. User selectable 4-20 mA, 0-20 mA or 0-10V levels. ... The supply can drive 20 mA into a 500 ohm (or lower) load for 10V compliance, or 10V into 5K ohm (or higher) load for 2 mA compliance.

The important point is that the output is conditional on the load resistance. (and the "or lower" bit probably means not less than 200 - 300 ohms, or the device will start malfunctioning)

I would have thought the AD DA solution would have been the best but at 300m the major problem would be pickup on the signal cable. Is it an electrically noisy environment? Intuitivley I would go for the best screened cable I could get and rout it well away from any other electrical cable and preferably in the ground!

 

[thepurple1]

You need to know if the pressure transducer is loop powered or powered externally.
i.e. loop powered is 2 a wire sensor and is powered by the controllers 4-20mA input.

If its not loop powered the 24volt supply is powered externally of the controller