pmascarenas
Member
i have studio 5000 v 24 and the processor is the L75, what i am trying to do is omit the ph controllers we use for waste water treatment. The new ph preamps from Signet Scientific now have an analog output of 4-20 ma which is equal to 0-14 ph. Original signet controllers you set the standard in a ph solution of 7 which should equal 0 mv. and slope it with a ph solution of either 4 or 10 ph.
ph of 4 equals 177 mv, ph of 10 equals -177mv. I think i need to scale my 4-20 ma back into mv with the range of 414.4 to -414.4 mv then in buffer solution of 7 i should read a mv signal close to 0 mv. but all ph electrodes will be off a little but due to age of the sensor, i have this part figured out at a ph of 7 to tare my signal back to 0 mv. the issue i have is in the buffer solution of 4 which should read 177 mv, if there is a difference in the mv reading i can use basically the same logic to get the mv difference from the sensor input versus the standard 177 mv for ph of 4. this would be my slope, problem i can't figure out is what to do with the slope mv difference so that the output of my scale block will be linear and read 4 ph and 7 ph or 10 ph when the sensor is in that solution or process material. any ideas would be helpful and appreciated thanks. link to my attached image. https://www.dropbox.com/s/7q8m8b6690pq868/ph standard.JPG?dl=0
ph of 4 equals 177 mv, ph of 10 equals -177mv. I think i need to scale my 4-20 ma back into mv with the range of 414.4 to -414.4 mv then in buffer solution of 7 i should read a mv signal close to 0 mv. but all ph electrodes will be off a little but due to age of the sensor, i have this part figured out at a ph of 7 to tare my signal back to 0 mv. the issue i have is in the buffer solution of 4 which should read 177 mv, if there is a difference in the mv reading i can use basically the same logic to get the mv difference from the sensor input versus the standard 177 mv for ph of 4. this would be my slope, problem i can't figure out is what to do with the slope mv difference so that the output of my scale block will be linear and read 4 ph and 7 ph or 10 ph when the sensor is in that solution or process material. any ideas would be helpful and appreciated thanks. link to my attached image. https://www.dropbox.com/s/7q8m8b6690pq868/ph standard.JPG?dl=0