pH and Temperature Electrode Possibilities

I have used a few different brands, some with little success and some with a lot, on a wastewater plant some time back. I suggest you buy separate pH and Temperature transmitters and wire the 0-10V analog output back to your PLC.

For pH, I recommend the ABB 4600-series instruments - these are easy to set up and use, but the probes are a bit bigger than your spec (6.1" long and

1.1" wide) To be fair, ABB do have a range of lab electrodes that are smaller than this, but they are glass and a lot less rugged. (Do a Google search on "ABB 4630 pH")

For Temperature there are a few companies to choose from - I would recommend you start with Rosemount, but ABB sell temperature transmitters too...

Hope this helps, Cameron:-)

Any suggestions on temperature transmitters? I am looking for a low cost solution for a few dozen temperature sensors. My system is VME based, but there is very little available for temperature measurment in VME cards. So I am looking for a transmitter which can (idealy) provided a

0-10 V linear analog out to feed to a VME A/D board. My temperature range of interest is only 20-100 C and I'd like resolution of 0.1 C, so I'm looking towards thermistors. The sensors need to be surface mountable, small, non-magnetic and be located in a radiation-controlled area. The transmitter can be located outside the radiation shielding if needed.

Anyone have any suggestions?

Thanks,

-- Steve

Got any digital i/o?

-Mike-

Mike--

Actually, I have nearly 500 DS1820 digital thermometers in "1-wire" networks using ascii RS-232 to 1-wire adaptors. These don't have quite enough resolution for this particular application. Moreover, they have proven to be very unreliable for us (not the sensors themselves so much as the 1-wire network). This is at least partly to do with poor installation on our part, but our overall experience has been bad enough that we are unwilling to invest more into these.

Some more details on our setup: this is a particle accelerator (electrons) facility. These temperature sensors are a first line of machine protection for electromagnets, UH-vacuum beam pipes, an RF system, etc. The control system is already in place (primarily VME based) which can provide archival, alarm notification, remote display, etc. I'm looking for a few dozen temperature sensors (20-100 C, 0.1 C resolution) with a reasonably easy way to interface to our control system. A sensor -> VME module would be ideal, but sensor -> transmitter (0-10V) -> VME A/D would be good (already have the VME A/D available).

Thanks,

GLI (Great Lakes Inst) and Hach I think both have pH instruments which also put out the stream temperature, both as 4-20ma. You need the temp to make properly corrected calulations or interpretations of the pH readings.

4-20 mA is the standard for transmitters. Put a 250 ohm resistor at your input. Place a 24 VDC power supply in series with your transmitter and then run it to the resistor. Connect the negative of the power supply to the neutral of the AI. Now you have a standard 1-5 VDC signal. Ignore any values outside this range.

Try the Omega catalog for a great range of relatively cheap instrumentation including pH and temperature transmitters.

0.1 C resolution is pretty tough to get. A direct 3- or 4-wire RTD input would be much better.

Walter.