how to calibrate Hach sc100 analog outputs

[defcon.klaxon]

Hi all,

Recently a client had an issue with their Hach sc100 and while I got the instrument back up and running, the analog outputs for the two turbidities are off, and I'm really perplexed on how one actually calibrates the 4-20mA loops.

In the setup menu I have found where you can adjust the 4mA output, and then the 20mA output but the numbers you adjust are entirely nonsensical. The 4mA "adjustment" is a number like 55,747 but the 20mA "adjustment" number is like 10,343. I have no idea what these numbers represent, how to adjust them, and why the 4mA number is much higher than the 20mA number.

I've read through the manual and absolutely nothing is described, all it says is yeah, that's where you adjust but no procedure and no explanation for what I'm looking at.

Strangely there is a procedure on Hach's website for the sc200, but the numbers don't match; what I mean is, the actual value is still cryptic but you are you adjust that number until your 4mA and 20mA are set, and the higher the number the higher the output.

Anyway, thanks for any help, I've got an email into Hach tech support but I have no idea when they'll get back to me and I'd like to tell the client sooner than later than I've got something to try.

 

[JTCat]

Hi,
Ensure the sensor code for the sensors are correct in the Hach SC100 controller.
This is under the configuration menu.
Under sensor setup you can select calibration, and it will walk you through the calibration.
I used to calibrate these every couple of weeks.

It's easier to make the adjustments in a PLC as to what the analog values mean to you, rather than mess with the offsets and adjustments in the SC100 controller.
As long as you maintain proper calibration of the sensors you should be able to do everything you need through the PLC.

 

[defcon.klaxon]

As long as you maintain proper calibration of the sensors you should be able to do everything you need through the PLC.

True, but the issue here is that it was working just fine, then it had some sort of power failure, and now that it's back working the 4-20mA signals are not correct. As far as calibration of the sensors, that is done by the water treatment operator on record. The local display shows the correct turbidity values, but the analog output loops are not.

 

[SledDog]

Seen this many times. We also have seen it when we go to generator power. It usually ends up that the SC100 has to be replaced because of the drift. It may be stable for awhile, but it will go out again. We send ours out for repair and the end result is Hach replaces the 4-20 output board.

Our operators also cal the units once a day. But we get the call when the unit reading does not match the SCADA reading.

Yes, the numbers make no sense. You can take care of it in the PLC, but when it drifts you will be working in the PLC again, and again.

In the SC 100 set the 4ma number, then the 20. You will need to go back and forth between 4 and 20 until you are good on both ends. The span changes every time you change either number. Easiest and fastest way is with a good 4-20 ma tool to read the values. Our guys can set the 4-20ma on one of these in under 5 minutes without accessing the PLC.