Importance of Getting the Detailed Data
The MicroTOL Turbidimeter manufactured by HF Scientific is used to monitor the influent and effluent turbidities of the laboratory flocculator setup. In the current experimental setup, we are obtaining data from each turbidimeter in increments of 1 second using Process Controller.
The MicroTOL Turbidimeter is outputing a light sensor, that is then translated into an electrical analog data set that can be read by the computer to output a NTU reading. The frequency of the analog data is a lot faster than 1s, and is averaging the data to give the user a reading every second.
For our experiment, we are trying to find the smallest changes in turbidity over the smallest amount of time. By looking at this "raw" analog data, we might be able to draw better conclusions about particle size and sedimentation than the analyses with the averaged data. We are currently in contact with HF Scientific to determine how to obtain this analog data.
Contact Log with HF Scientific, Inc. Technical Support
Friday, February 15th
Gemma talked with Phil/Joel in technical support. It is possible to get the "Raw Data" and we can do this by incorporating MODBUS communication programs. Phil does not know the exact timing of the analog signal, but he believes that is as low as 250 milliseconds (maybe even lower), however, he also said that we might not be able to get a clear enough (readable) signal until we reach 750 milliseconds. He will figure out the exact number and respond next week.
To read the raw data, we need to user Hyper Terminal, a Windows program that can bee accessed under Windows>Accessories>Communication. The HyperTerminal manual should be read to figure out exact settings/configurations to read from Modbus. Next, we have to buy the Modbus program package (or this might come free with HF Scientific software).
Monroe's comments: This is all digital data. We want analog data. We want voltage, not serial communication using MODBUS. We are already using the modbus (not sure on this terminology, but we are definitely using RS485 communication protocol) to get the data from the instrument. And I think we are already getting a data point every second. The process controller software uses serial communication (in a more sophisticated way than the hyperterminal approach) to get data from the turbidimeter. If we can get an analog signal then the meaningful data rate will only be limited by the detector (sensor) response characteristics. Check out: Floc Strength Measurement
Wednesday, February 21
Spoke with Joel and Mike Goodman (Director of Technical Support). There are two ways to get the raw voltage data.
1. Obtain the voltage before it goes into the ADD. These numbers will be 0-3 Volts and we will need to associate the voltage with an NTU number. We could also try hooking up a data logging voltmeter to this.
2. Download a version of MODBUS POL, a shareware program that will get the voltage data converted into NTU data. The program can get data every 150 millisecond, but using MODBUS POL, we will only be able to retrieve as fast as the HF can update it, which is approximately 250 millisecond. The digital numbers can be dropped into csv file and into excel easily. Joel was saying that we might not need MODBUS POL if we have a program that is retriving data (Process Controller). I think we need to distinguish the functions of MODBUS and Process Controller to see if PC can accomplish what we need.
Mike will be sending us an email with all of these specifics written out on different ways we can retrieve a faster signal.
Monday, March 10
Mike sent the information on how to access the data:
The attached photo shows the connections that will give you the voltage as
it is presented to the A/D. These are real time readings that have not been
linearized or massaged at all by the CPU. There are logging voltmeters that
can be connected to serial ports. I'm sure Cornell has these around
somewhere.
The other method that we discussed was to log the data via modbus. We use a
program called Modbus Poll. I have provided the link below. The cost is $99
for a single license, but it is free fro a limited period, I'm not sure how
long that period is.
http://www.modbustools.com/index.asp
If anyone there knows programming and is familiar with modbus they can write
something to get the data.
The modbus addresses (registers) of interest are:
30001 & 30002 Float Type = Sensor reading
30003 & 30004 Float Type = Sensor Raw reading
These are duplicated at :
40031 & 40032 for Sensor reading
40033 & 40034 for Sensor Raw Reading
I have attached a modbus manual for the Micro TOL.
If you need RS485 converters we use B & B (bb-elec.com) For RS485 to RS232 we recommend Part #485D9TB
$74.95 for RS485 to USB we recommend Part # USOTL4 $139.95.