Report: Evaluation of T-Hydronics TH-LD Submersible Pressure Transducers To: "E - All WRD Employees" Subject: Report: Evaluation of T-Hydronics TH-LD Submersible Pressure Transducers Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Date: Fri, 10 May 1996 15:58:36 -0500 From: "Dorothy E Greenwood, Secretary (Steno), Bay St. Louis, MS" Evaluation of T-Hydronics TH-LD Submersible Pressure Transducers [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 obtained from the actual unit tested.] The HIF recently completed an evaluation of two T-Hydronics Model TH-LD submersible pressure transducers. The purpose of the evaluation was to determine whether these devices meet manufacturer specifications and WRD requirements. The results are summarized in this report. General Description The T-Hydronics TH-LD pressure transducer is designed to determine the water level in a well or borehole. It consists of a stainless steel housing (1.5 inches in diameter by 2.75 inches long) that contains the transducer element and electronic circuitry and a PVC-jacketed vented cable. Operating range of the units tested was 0 to 10 pounds per square inch (psi) (0 to 23.1 feet). [NOTE: Other ranges from 0 to 5 psi through 0 to 500 psi are available.] These units also have temperature compensation for -18 to 65 degrees Celsius and an analog voltage output of 0 to 3 millivolts per volt (mv/V) of the operating voltage. The manufacturer's stated combined error for nonlinearity, hysteresis, and repeatability for the pressure transducer is 0.5 percent of the full scale output. For a 0 to 23 foot (10 psi) pressure transducer, this is +/- 0.11 foot. Over pressure ratings are 1.5 times the full scale. Nominal operating voltage is 10 volts ac or dc. Test Procedures Standpipe test procedures The sensors were tested in a 100-foot standpipe facility located at the HIF. A Campbell Scientific, Inc. CR10 data logger connected to a Paroscientific PS- 2 was used as the controller for the cycling of the water level in the standpipe. Based on the sensor being tested, the CR10 was programmed to raise and lower the water level in the standpipe in four- or five-foot increments over a range near that of the full-scale range of the sensor. Three temperature sensors also connected to the CR10, monitor the temperature of the water in the standpipe during the test. The T-Hydronics TH-LD sensors were suspended by their cables and placed approximately 22 feet from the top of the standpipe. Since the T-Hydronics TH-LD sensors produce an analog voltage output, they were connected to a second CR10 with analog voltage inputs (the primary CR10 analog inputs were used by the standpipe temperature sensors). The secondary CR10 was programmed to excite the sensors with 2.5 volts ac (Campbell's ac bridge measurement) and collect and store the average of ten analog voltage measurements every 30 seconds. This CR10 was also programmed to communicate with the primary CR10 as an SDI-12 sensor. After completion of setup, the CR10 was set to begin automatic operation. Data was collected over telephone modems during the test periods. At the end of each sensor test period, the automatic operation was shut off and the water level again set to the midpoint of the range of water levels and the sensors checked for any offset in readings. The test ran for six cycles from October 11 to 14, 1995. Ambient water temperature of the standpipe during the tests was between 22.5 and 28.4 degrees Celsius. Environmental chamber test procedures Two T-Hydronics submersible pressure transducers model TH-LD were tested in the environmental chamber. A National Institute of Standards and Technology (NIST) traceable pressure standard was used to measure the standard applied pressure that simulated the water level. For one transducer, a standard pressure equal to 0 to 23 feet (at 20 different water levels) was applied at four constant temperatures. For the other transducer the same pressures were applied at five constant temperatures. The pressure transducer measurements were recorded using a Campbell CR10 data logger and a SM 192 data logger. A constant 12 volts was supplied during the environmental testing. The pressure transducer analog 3 mv/V output was translated to feet of water using linear regression to define the equation for each constant temperature. Test Results Standpipe test results The summary of the test results of the transducers is displayed in table 1. Figure 1 showing graphs of the test results is available upon request. Environmental chamber test results At constant temperature--Figures 2 and 3 (available upon request) represent the measurement differences from the standard at constant temperatures of 25, 0, 50, and -5 degrees Celsius for both of the transducers. Table 2 summarizes the results of the differences from the standard values for the two units at constant temperatures under pressure cycling. The differences between standard values and measured values are grouped in two ranges: 0 to 10 feet and 10 to 23 feet. For S/N 34952, in the 0 to 10 foot range, the largest span of difference from a minimum difference to a maximum difference was -0.08 to 0.06 foot. For S/N 35415, in the 0 to 10 foot range, the largest span from a minimum difference to a maximum difference was -0.11 to 0.13 foot. For S/N 34952, in the 10 to 23 foot range, the span from a minimum difference to a maximum difference was -0.10 to 0.08 foot. For S/N 35415, in the 10 to 23 foot range, the span from a minimum difference to a maximum difference was -0.18 to 0.13 foot. Zero Reading--For one unit the difference from the standard measurement, when referenced to atmospheric pressure, ranged from -0.06 to 0.06 feet of water. For the other unit the difference ranged from -0.10 to 0.01 feet of water. Measurement hysteresis--For S/N 34952, the largest pressure measurement hysteresis was 0.03 foot. The largest pressure measurement hysteresis for S/ N 35415 was 0.07 foot. Comments When a pressure transducer is used for measuring water level, the following factors need to be considered: A regulated constant voltage supply is required to maintain the accuracy of reading for an analog voltage output transducer. The data recorder and pressure transducer need to be calibrated as a system and always used as a unit. This ensures that the measurement error of the transducer and the error of the data recorder analog to digital conversion are combined and known. If necessary, the proper linear regression equation can be programmed into the data recorder and used to help correct the measurement error of the system. Conclusions Standpipe conclusions The differences between the TH-LD's and the PS-2 at the temperatures tested were in the range of -0.31 to +0.28 feet, mean values were in the range of - 0.10 to +0.04 foot. There was no discernable hysteresis based upon rising or falling stage. Environmental chamber conclusions Accuracy--Test results indicate that measurement differences are as much as 0.18 foot. For both transducers in the 0 to 10 foot range, test results indicate that measurement differences are greater than 0.01 foot. For the 10- to 50-foot range, measurement differences were greater than 0.1 percent of reading for both transducers. (See table 2.) Zero Setting--When the pressure transducer is vented to atmospheric pressure, the measurement can not be set to a zero value. Zero Reading--When repeatedly vented to atmospheric pressure, the transducers do not measure the same value. The values varied as much as 0.12 foot. Measurement hysteresis--During pressure cycling, the pressure transducers did not repeat the same measurement for both applications of the same standard value. SDI-12 Communication--These pressure transducers do not have SDI-12 communication. These units have analog millivolt output. Table 1. Standpipe Tests--The range of differences and mean of the differences between two model T-Hydronics TH-LD submersible pressure transducers and a PS-2, in feet of water. PS-2 Stage, S/N 34952 S/N 35415 feet Mean Range Mean Range 0.00 -0.04 -0.27 ~ 0.18 -0.01 -0.20 ~ 0.19 4.00 -0.05 -0.21 ~ 0.18 0.00 -0.07 ~ 0.22 8.00 -0.06 -0.25 ~ 0.21 0.01 -0.06 ~ 0.28 12.00 -0.02 -0.25 ~ 0.18 0.02 -0.09 ~ 0.24 16.00 -0.03 -0.26 ~ 0.17 0.02 -0.11 ~ 0.23 20.00 -0.07 -0.28 ~ 0.12 0.03 -0.19 ~ 0.08 16.00 -0.06 -0.25 ~ 0.06 0.04 -0.08 ~ 0.13 12.00 -0.08 -0.27 ~ 0.03 0.03 -0.07 ~ 0.13 8.00 -0.09 -0.28 ~ -0.02 0.02 -0.09 ~ 0.09 4.00 -0.10 -0.31 ~ 0.02 0.01 -0.16 ~ 0.06 0.00 -0.06 -0.27 ~ 0.12 0.01 -0.20 ~ 0.09 Table 2. Environmental chamber test-- Minimum, maximum, and mean difference, in feet of water, between standard values and values measured by two T-Hydronics model TH-LD submersible pressure transducers in two water level ranges and at the listed temperatures (S/N, serial number; Min, minimum; Max, maximum; ft, foot) _____________________________________________________________________________ S/N, Temperature, in degrees Celsius Water level -20 -5 25 50 0 Sensor 34952 Min. -0.06 -0.05 -0.05 -0.08 -- 0-10 ft Max. 0.06 0.04 0.07 0.06 -- Mean -0.00 -0.00 -0.00 -0.00 -- Sensor 34952 Min. -0.09 -0.07 -0.10 -0.04 -- 10-23 ft Max. 0.08 0.05 0.08 0.04 -- - Mean 0.00 0.00 0.00 0.00 -- Sensor 35415 Min. -0.11 -0.10 -0.06 -0.04 -0.10 0-10 ft Max. 0.13 0.12 0.08 0.04 0.11 Mean -0.01 -0.01 -0.01 -0.00 -0.01 Sensor 35415 Min. -0.18 -0.17 -0.12 -0.06 -0.16 10-23 ft Max. 0.13 0.12 0.09 0.06 0.11 Mean 0.01 0.01 0.01 0.00 0.01 For more information on the standpipe testing call Carl Scott (CTSCOTT) at (601) 688-1538, or for environmental chamber testing information, contact Trudy Olive (TEOLIVE) (601) 688-1558.