REPORT--Evaluation of Digital Data Recorders To: "E - All WRD Employees" Subject: REPORT--Evaluation of Digital Data Recorders Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Date: Wed, 07 Feb 1996 15:05:34 -0600 From: "Dorothy E Greenwood, Secretary (Steno), Bay St. Louis, MS" EVALUATION OF FOUR SUTRON 8400 DIGITAL DATA RECORDERS (Note: This evaluation is intended for internal USGS reference purposes only and does not constitute acceptance or rejection of the brand name product on the basis of the results of the actual four units tested.) The HIF recently completed laboratory evaluation of four Sutron Model 8400 DDR (Digital Data Recorders). The purpose of the testing/evaluation was to determine whether these sensors meet manufacturer specifications and WRD requirements. The results are summarized in this report. GENERAL DESCRIPTION The Sutron 8400 DDR was designed for drop-in replacement for analog to digital recorders (ADR's). The Sutron 8400 DDR uses the same steel tape or beaded cable, float wheel, float and counterweights that are used with the USGS ADR's at stilling well sites. Data viewing and system parameter setup can be performed using the front panel display and key pad or a computer through the RS-232 interface. Downloading data stored in the Sutron 8400 memory can be performed by using the PCMCIA data retrieval card or a laptop computer. When the setup parameters have been changed, the change is time tagged and recorded into memory. If the Sutron 8400 perceives a change of stage greater than 9 feet per second or some other malfunction (such as loss of external power), an error message will appear as a "?" in front of the recorded data. The internal lithium battery saves only the setup values and data previously stored into memory if external power is lost. MANUFACTURER SPECIFICATIONS Pulleys Supported Size Range Accuracy 1.0 ft 655 ft 0.01 ft 1.5 ft 982 ft 0.015 ft Internal memory capacity: 12,000 readings internal, expandable to 50,000 readings. Recording Intervals: 1 second, 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, and 60 minutes. Operating Temperature: -40 to 60 degrees Celsius Humidity: 0 to 100 percent Power requirement: 9.5 to 15 volts Power Consumption: less than 1.3 mA (logging at 15 min. interval) Data Retrieval Card Optional capacities: >60,000 readings (256 kb) >240,000 readings (1 mb) TEST PROCEDURES Four Sutron 8400's were tested in the environmental chamber. Pendulums were attached to the shaft encoders. The known inputs by shaft rotation were compared with the display measurement, the computer real time measurement, and the measurement recorded into the 8400 memory. The detailed procedures are as follows. 1. Temperature cycling -40 to 60 degrees Celsius--The chamber temperature was programmed to change 20 degrees Celsius in one hour from one temperature setting to the next. Each of the constant temperatures was held two hours. It took 30 hours per cycle and 5 cycles were used. 2. Accuracy of the shaft encoder measurement at various constant temperatures--The shaft rotations were performed after the internal temperature of the units was +/- 2 degrees Celsius of the chamber temperature for one hour. The pendulums attached to the shaft encoders were manually rotated at constant temperatures of -40, -20, 0, 20, 40, and 60 degrees Celsius. 3. Data record a. Time series--Set recording time interval and collected data at 1 second, 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, and 60 minutes. b. Time tagging--Observed whether the data recorded into memory was date and time tagged. c. Storage capacity--Set recording interval to 1 second. Counted how many entries were recorded into memory before the first entry was overwritten. 4. Data retrieval card--At each constant temperature, 4 data retrieval cards were used to extract the data record accumulated since the last data retrieval. One card was dedicated to each test unit. A data card reader connected to a computer was used to examine the data files on the data retrieval cards. The data retrieval card files were examined for a. Date and time tagging. b. Accuracy and completeness of recorded measurement as compared with data stored in 8400 memory. c. Capacity of data storage used. 5. RS-232 communication--The RS-232 ports on the four test units were connected to a computer outside the chamber. The computer was used to monitor the water level measurements corresponding to shaft rotations, water-level recorded into Sutron 8400 memory, the setup parameters, and to reset the level when necessary. 6. Clock accuracy--The test units real time clocks were set at the beginning of the testing to agree within 2 seconds of a time standard. At the end of the temperature testing the clocks were compared with WWV time standard. 7. Condensation--The test units were taken out of chamber at -12 degrees Celsius. Condensation formed on the cases. The units were left at room temperature overnight (16 hours) with the external batteries disconnected. RESULTS 1. Temperature cycling--Two of the test units (A and B) had no measurement difference from input during temperature cycling. The test results indicate that unit C had measurement difference from input of +0.01 and +0.02 foot during 1 of the 5 temperature cycles. Also that unit D had measurement difference from input fluctuations of +/- 0.01 foot, and random "Shaft Overspeed" messages that occurred at all temperatures. Unit D was checked again. It had a measurement difference from input of -0.04 and -0.05 foot for 1 of 5 temperature cycles and random "Shaft Overspeed" message. Units C and D were returned to the manufacturer for repair. The manufacturer replaced a defective clock chip in unit D. Two units (C and D) were retested with unit A as the control. The test results indicate that all three units didn't have a measurement difference from the input value throughout the -40 to 60 degrees temperature range. 2. Accuracy of the shaft encoder measurement at various temperatures-- Units A and B had no difference in measurement from input at constant temperatures of -40, -20, 0, 20, 40, and 60 degrees Celsius in response to changes in water-level input. Unit D readings fluctuated by +/- 0.01 foot after the completion of manual shaft rotations. This occurred during all manual inputs of data and at all of the constant temperatures. The "Shaft Overspeed" message did not occur in response to manual shaft rotations. Unit C had no difference in measurement from input in response to manual shaft rotations at the constant temperatures. Units A, C, and D were retested after manufacturer repair. They had no difference in measurement from input at constant temperatures of -40, -20, 0, 20, 40, and 60 degrees Celsius in response to changes in water-level input. Unit B was not retested. 3. Data record--Date and time tagged water-level measurements were stored into memory at various time intervals. The Sutron 8400 memory storage capacity was greater than 12,000 readings. 4. Data retrieval card--The cards retrieved accurate, complete, date and time tagged water-level measurements from the Sutron 8400 memory at temperatures ranging from -40 to 60 degrees Celsius. A total of 25,000 readings used 72K of available 256K card memory capacity. 5. RS-232 computer interface--Communicated with computer and performed all required functions at -40 to 60 degrees Celsius. 6. Clock accuracy--Ranged from 2:29 minutes lost to no time lost during 7 days of the first testing. Clock accuracy after repair--The maximum difference of the internal clocks with the time standard was +4 seconds during the two retests. During testing after the manufacturer replaced the clock chip in Unit D; the previously observed measurement differences, time lost, and "Shaft Overspeed" messages did not occur. 7. Condensation--The condensation didn't affect the operation when power was reapplied. COMMENTS Removing the backup battery erases the memory and setup parameters. The Sutron TS8400 software is necessary when using a computer to communicate with the 8400. The Sutron TS8400 program is easy to use for setting up/changing operating parameters, viewing the data stored in memory, viewing real time water-level measurements and retrieving data. A PCMCIA card reader is necessary to retrieve data stored on the PCMCIA card. For proper operation, the unit needs to be connected to a properly installed low resistance gagehouse ground. This is particularly important if the tipping bucket raingage is connected to it. When the 8400 is ordered from Sutron the float wheel is not included unless specifically requested. CONCLUSION During the initial tests, two units showed some difficulties as indicated by the test results. However, after manufacturer repair, the units were retested and functioned properly. The following is a summary of the findings. 1. Temperature cycling accuracy--During retest, the units had no difference in measurement from a constant input for the temperature range of -40 to 60 degrees Celsius. 2. Various constant temperature accuracy--During retest at 5 constant temperatures ranging from -40 to 60 degrees Celsius, the units in response to varying inputs had no difference in measurement from the input. 3. The replacement of the clock chip in unit D corrected the measurement difference, clock error, and the "Shaft Overspeed" message. 4. Data collection, storage, and retrieval using the data card or computer performed as expected at temperatures ranging from -40 to 60 degrees Celsius. For more information contact Trudy Olive (TEOLIVE) at 601-688-1558.