Maintenance and Field Tests of the WTS-Tr
Because the instrument is typically submerged in seawater from four months to one year, maintenance and testing of the mechanical and software capabilities prior to deployment is critical. In addition to the basic maintenance operations outlined for the WTS-Tr in the McLane Laboratory manual, additional recommended maintenance procedures developed by members of the USGS Massachusetts Bay field program are presented below.
Inspection and Maintenance Procedures of the Exterior Controller Housing
Inspect the exterior of the anodized aluminum controller housing and end caps (Figure 1A) for overall integrity. Small scratches, corrosion, and pitting of the housing and end caps may be covered with a marine grade epoxy. Depending on the size and depth of the repaired surface, this may only be a temporary remedy. The area should be periodically re-examined to monitor further migration of corrosion, and the end caps or housing replaced if warranted.
- Examine the four bulkhead connectors for areas of corrosion and pin integrity. The pins should be cleaned with a wooden swab (Q-tip) sprayed with an electrical cleaning solvent (i.e. "Contact re-nu"). Avoid contact with the O-ring on the connector with the cleaning swab.
Replace the connectors if the pins are severely corroded or missing.
- Apply a light coating of electrical insulating compound, such as Dow Corning 4 (DC 4), to the pins and shoulder O-ring of each of the bulkhead connectors, and cover each connector with a dummy plug. Inspect the two external zinc anodes on the end caps and replace if they show significant deterioration.
Inspection and Maintenance Procedures of the Internal Controller Housing
- Unscrew the three 1/4" x 20 hex head bolts and attached shoulder insulators from the bulkhead connector end cap. Inspect, clean, and re-grease the hardware (bolt threads) with DC 4 and/or replace as warranted.
- "Gently" work the end cap free by rotating and pulling it away from the housing. A flat blunt hard plastic or wooden spatula may be used to gently pry the end cap from the controller housing until removal by hand is accomplished. Use of metal to pry the end cap may damage the anodized aluminum surface and promote corrosion.
- A frame containing the electronics package is attached to the end cap; slide the electronics out of the case and onto a clean work surface covered with plastic or laboratory grade absorbent sheeting.
- Continue the inspection of the controller housing by shining a light inside the housing and examine for signs of water intrusion, corrosion, and general cleanliness. Generally, a few blasts from a laboratory canned air source are sufficient for removal of any small foreign objects or dust particles within the housing. The flat surface of the housing where the end cap meets and is through-bolted may be cleaned with a laboratory wipe (Kim wipe) and its circumference lightly lubricated with DC 4 compound. Check the three threaded bolt holes for general cleanliness and pitting or corrosion.
- The electronics package contains three stacked controller boards and a power supply. Schematics are described in detail in the McLane Research Laboratories User Manual (1992). Remove the face and radial O-rings located on the inside shoulder of the end cap. Inspect, clean, and replace (if necessary) and lightly lubricate with silicone grease such as DC 4. Swab the grooves of the O-ring housings with a Q-tip prior to re-seating the O-rings.
- The power supply consists of a stacked set of alkaline D-cell batteries wired in series and housed in a frame below the electronics boards. The voltage of a new battery package is approximately 31.5 volts and is exclusively provided by McLane Laboratories. The battery should be replaced when the voltage reads less than 20 volts or if the user desires ( i.e. prior to a field deployment). Battery capacity depends heavily on temperature, cell integrity, duty cycle and user programming of the field parameters. Typically only a three to four volt loss of capacity is apparent during a four-month winter deployment in Massachusetts Bay.
- To replace the battery, disconnect the battery lead from the bottom controller board and remove the three small screws from the bottom plate of the frame holding the battery package and remove the battery. Secure the new battery into the frame, reattach the plate and screws to the bottom plate and reconnect the lead to the bottom controller board.
There may be a nine-volt backup battery located near the top of the electronics package as well. This battery provides enough power to access the WTS unit and recover any stored data in the event the main power supply fails during a deployment. This should also be replaced with a new nine-volt battery prior to deployment.
Both the 31.5-volt and 9 volt batteries should be tested under a load with an in-line 100-ohm/10 watt resistor attached to a DC voltmeter prior to installation. New batteries should be installed prior to any laboratory or field-testing procedure. These same batteries may be used for actual field deployment provided that the voltage is greater than 30 volts for the main battery.
A small package of laboratory desiccant may be attached to the electronics package frame to absorb any excess condensation that may form during the length of the deployment period.
- Carefully insert the electronics package with the attached end cap and slide it into the housing until the bolt holes align and the end cap seats at the face of the housing. Attach a communication cable to the communications bulkhead connector and attempt to access the instrument.
Occasionally, the user will be unable to access the WTS software even after proper cable connection and software commands have been verified. Slide the electronics package out of the housing and disconnect the main power supply and 9 volt battery for about thirty seconds to recycle the power. Reconnect the batteries and attempt to communicate with the instrument. This procedure is usually successful in re-establishing communication with the instrument.
If recycling the power does not re-establish communications with the WTS, contact McLane Laboratories for assistance. Typically this is resolved with a new battery pack, however there have been instances where replacements of diodes and the central processing chip have been necessary.
The WTS-Tr contains "volatile memory" and if this "rebooting" procedure is undertaken after actual data has been collected from a test or field deployment, the data will be erased.
- Complete the installation of the end-cap to the housing by reinstalling the plastic insulator into the bolt hole on the end cap. Overlay this with the flat and lock washers and thread the bolt through the end cap into the housing. Tighten each bolt systematically and only until the lock washer becomes flattened.
Maintenance Procedures of the Pump Assembly
The pump assembly consists of the stepper motor, manifold, tubing, gear pump and filter holders as displayed on Figure 1A. Prior to testing and deployment, a general inspection of the entire assembly's components for cracks, scratches, oil level, and general integrity is recommended.
- The silicone oil level contained within the pump assembly is evaluated by gently squeezing the rubber bladder located on the underside of the stepper motor. The oil level is low if the rubber bladder has lost its firmness and the internal motor windings can be felt through the rubber material. The oil should be replaced/refilled by McLane Laboratories.
- The manifold should be inspected for overall integrity. The 1/4" tygon tubing, plastic tube fittings, and couplings that mount filter holders to the manifold should be replaced if worn or degraded.
- The head of the graphite gear pump should be removed and the internal gears replaced prior to each deployment. A four-pronged magnetic coupler, which mates with the slotted drive gear in the pump head, sits in a recessed "well" of the motor body. This should be removed, cleaned and the "well" swabbed out and flushed out with distilled water. Any particulate matter that remains in the "well" may cause the coupler and gears to slip during pumping operations. This may result in invalid volume measurements during a pump event. An indication of such a problem will result in an error message ("pump has slipped") when the user is downloading the data during real-time testing procedures of the instrument prior to field deployment.
The gear pump head contains a radial O-ring, which should be inspected, cleaned and lightly coated with a silicone compound such as DC 4. The head and housing should fit carefully together so the four pins on the coupler seat properly in the corresponding slots of the driver gear in the pump head.
An oil filled bladder similar to that of the stepper motor is located on the bottom of the motor body and should be inspected and refilled if necessary.
- The eighteen plastic filter holders, internal gaskets, and associated hardware are cleaned according to laboratory specifications and replaced if damaged. USGS scientists typically use pre-weighed polycarbonate 47mm x 0.4um pore size Nucleopore filters for the Massachusetts Bay Program. The filters are stored in petrie dishes then loaded into the filter holders prior to deployment.
Specialized white plastic cylindrical tips (0.68 inches in diameter, and 0.68 inches tall) containing Bis (tributyltin) oxide are installed on the ends of each filter holder to retard biofouling at each intake orifice prior to long-term field deployment. These tips should be handled with laboratory gloves in accordance with other precautions identified in the Material Safety Data Sheet.
Depending on their condition and on the duration of the past and future deployment schedule, one should consider replacing the eighteen quick disconnect female couplings that secure the filter holders to the circular frame.
Laboratory Setup of the WTS-Tr Instrument Using the Transmissometer as an External Sensor
The setup and configuration of this testing procedure is as follows:
- A communication cable attached to a laptop computer is connected to the six-pin communications connector of the controller housing that allows access to the instrument. The user may view the input and responses of the WTS-Tr instrument's various menu and programming options during the testing and actual pumping procedures. For each option, the menu driven format will prompt the user for specific information.
The components for the test are shown in Figure 4. The controller housing and pump assembly are immersed in a fresh water test tank to a depth sufficient to slightly immerse the filter holder couplings. A length of 1/4" Tygon tubing is connected from the gear pump motor discharge port into a three liter plastic graduated cylinder that is located outside the test tank. This is designed to collect the volume of water pumped for each successive event.
- The external transmissometer should be connected to the appropriate four-pin bulkhead connector on the WTS-Tr controller housing prior to immersion in the test tank. The interaction of the transmissometer with the WTS-Tr unit may be evaluated at this stage of testing.
The transmissometer remains outside of the test tank, as it requires external power. In this case a USGS "MIDAS" instrument (a multi-parameter intelligent data acquisition system) supplies the power. The MIDAS system is used in conjunction with the WTS-Tr instrument as well as other instrumentation for collection of oceanographic data in the Massachusetts Bay field program.
- After establishing communication with the WTS-Tr pump142 software a DOS pipeline file is recommended so as to save all commands and responses to a file.
The Main Menu and Deployment of the WTS-Tr in the Laboratory Using the Transmissometer
The main menu listing (Figure 2) of the WTS-Tr is detailed below in order to familiarize the user with the functions and deployment parameters of the instrument:
- A check of menu item 1 will determine if the current time and date are correct. Any changes may be made at this stage.
- Menu item 2 allows the user to review the current diagnostic features of the WTS-Tr instrument (Figure 2). As the data scrolls on the screen the following parameters are displayed: time/date, voltages (both the main battery voltage of approximately 31.5 volts and the unregulated voltage of approximately 8-9 volts). The transmissometer voltage (when connected in ambient conditions) should display a reading of approximately 4.0 to 4.5 volts in air).
- Menu item 3 tests the pumping action at the various ports of the instrument. The position of the valve may be determined by observing the location of a notch in the valve stem at the top of the pump head manifold. The notch indicates the valve alignment with each port/filter holder. Typically the desired pumping parameters are entered and a pumping sequence for a selected port is initiated. The user may wish to test some or all of the ports independently at this stage of the testing procedure.
The unrestricted volume (as there are no filter holders attached to the manifold head) from each port is collected in the graduated cylinder and the volumes matched against those from the initial input. The collected volume should agree within 8 percent of that displayed on the computer screen.
After any testing is completed and prior to deployment, the valve should be aligned at position "one (home)". The pump cycle begins by first pumping at port #1 and then sequences to the next port in a clockwise rotation. If eighteen ports are programmed for deployment, the valve should cycle to each port and become re-aligned at position 1 (home) after the deployment sequence is completed.
- Menu 4 (move valve) tests the mechanical movement of the valve as the user sequences it from one port to the next. A smooth movement of the valve stem should occur without any audible chatter and the notch should line up with the next port.
- The pre-load filter routine (menu 5) is used to prime the filters within the filter holders but is not typically used by the USGS scientists prior to testing or field deployment procedures. Each filter holder is individually primed by hand, from the back end of the filter holder, using a syringe filled with distilled water.
- The "create schedule routine" (menu 6) lets the user enter a deployment schedule and is run automatically when menu 7 (run schedule and deploy) is selected.
- Menu 7 allows the user to program the WTS-Tr for deployment. The user will be prompted for all inputs required for proper instrument operation.
A typical schedule that is used by USGS scientists for both laboratory testing and actual field deployment in Massachusetts Bay is shown in Appendix 1. Generally, a one to two-week deployment schedule using these field parameters is performed during testing in the laboratory. If desired, the input option: "number of summed transmissometer intervals" may be reduced from 128 in order to further the deployment program.
- After the instrument is deployed in the test tank and a scheduled sampling event has occurred, an optical filter (52 mm diameter, NDx4) is introduced into the light path of the transmissometer for a period of approximately eight hours in duration. This time has been calculated from the sampling rate of the transmissometer and the "number of summed transmissometer intervals" in conjunction with the "number of storms to sample" as shown on Appendix 1.
The filter attenuates the light beam of the transmissometer to an analog voltage of less than 1.5 volts (a typical threshold value of 3.5 volts is used by the USGS in field operations in Massachusetts Bay). This procedure simulates a sediment resuspension event by a storm.
As the filter remains in the light path of the transmissometer, the trends of the voltage are monitored and averaged over time by the internal software. As the time-averaged voltages decrease below the threshold value, the software initiates a sampling event. The first storm-sampling event ("storm found" as indicated by the software) automatically occurs near the end of the eight-hour time frame.
- After the sample has been pumped, the filter is removed in order to simulate a slow abatement of the storm. The time-averaged voltage readings from the transmissometer begin to increase. The middle (storm maximum found) and final storm (end of storm) sampling events are pumped as the threshold value is approached and then exceeded, respectively.
- After the test schedule is concluded, the results are downloaded from menu 8 and the data record may be evaluated. These include: timing of valve sequencing, total volume pumped, storm events recorded, battery voltage, and various other instrument functions.
This test evaluates the software and hardware responses of the WTS-Tr system and its response with an external sensor (transmissometer) to simulated ocean bottom resuspension events.
Although a fairly simplistic test, many system hardware problems such as improper valve sequencing, battery malfunctions, faulty transmissometer operation, gear pump slippage, and leaky manifold plates have been discovered during this phase of testing. In addition, much of the software operation during scheduled and simulated storm events may also be reviewed for proper performance. Any refinements or repairs to the instrument may be addressed at this time.
A Field Test Evaluating Additional Software and Hardware Functions of the WTS-Tr Instrument
Prior to each long-term field deployment in Massachusetts Bay, a test of the WTS-Tr instrument is conducted off the Woods Hole Oceanographic Institution dock facility (WHOI).
Ideally, slack water conditions would have been the preferred scenario for these field tests. However, a combination of space availability and scheduling issues at the WHOI dock, weather conditions, instrument repair schedules, field deployment schedules and tidal conditions ultimately determined the timing of these tests. Regardless, as the testing procedure have taken up to three hours to accomplish, the instruments were usually subjected to a range of tidal flow conditions. Slack water tidal conditions generally last for less than an hour at the WHOI dock facility.
The field test consists of:
- Assembling the WTS-Tr (without the transmissometer) in its test frame (Figure 6) with at least five pre-weighed filters contained in filter holders and attached to the manifold. The top perforated frits of the filter holders are removed from the filter holders because they have been shown to pre-filter the particles and cause erroneously low values (see Table 1 and Appendix 2).
- Three filter holders are attached to the manifold and allocated to collect suspended sediment samples in response to a short pre-programmed deployment schedule. No water is pumped through the remaining filter holders and these are used as controls. The remaining unused filter holder sites are plugged with plastic fittings to keep suspended material out of the pump system.
- A specially fabricated communication cable, approximately 33 meters in length, is attached to the communication connector on the WTS-Tr housing and back to the RS 232 data port on a laptop computer. This allows the user to program and view the scheduled pumping operations as they occur at depth in real time.
The WTS-Tr is lowered to its test depth of approximately 17 meters in the water column where the system is exposed to about two atmospheres of pressure. The overlying pressure helps dissolve and purge any remaining air from the system. The pressure also minimizes the potential for cavitation within the system that can affect the volume of seawater filtered onto the filter.
- A typical pipeline file is created to log user commands and the data stream resulting from the programmed pumping events.
Pumping events may be initiated from either: menu 3 (run pump motor) or by setting up a short-term deployment schedule (based on scheduled events only) from menu option number seven (run schedule and deploy).
A one-liter blood bag attached to the discharge port of the gear pump collects the volume of seawater pumped through the system (Figure 7). This volume is compared to the volume calculated by the computer software.
- After each pump event, the WTS-Tr must be raised to the surface, the volume from the collection bag measured and discarded, and the unit redeployed to the same depth prior to the next scheduled pump event.
- In order to evaluate the relative concentration of suspended matter collected by the WTS-Tr instrument, a Niskin bottle (a standard oceanographic water-sampling device) is lowered to the same water depth as the WTS-Tr instrument. The Niskin bottle collects a water sample as each scheduled pump event of the WTS-Tr instrument takes place.
Upon retrieval, the sample is drained into a plastic container from the bottom fitting of the Niskin bottle. The bottle is shaken several times during this procedure to ensure the removal of settled material from the bottom and internal surfaces of the bottle. The sample is filtered in the laboratory and the concentration of suspended matter compared to that collected from the coincident sampling period of the WTS-Tr instrument (Rendigs and Commeau, 1995). Results of these tests are shown in Table 2 and Appendix 3.
Software and mechanical operations which may be monitored during each pumping event include: sequencing of the valve to the next port, the functioning of the gear pump motor, reduction in motor speed as the filter becomes progressively clogged over time, proper shutdown procedures as each threshold value of volume or as minimum flow shutoff thresholds are achieved, and proper storage and downloading of the data file as the test is completed. Additional functions such as: total flow rates, the total volume pumped, and adjustments of the gear pump's motor speeds over time are also observed.
This test simulates scheduled pump events by the WTS-Tr instrument utilizing the field parameters used in Massachusetts Bay. This real time information has proved invaluable for quality control and for identification of mechanical and software problems associated with the pump system at depth within the water column.
Field Deployment and Recovery of the WTS-Tr Instrument From Massachusetts Bay
For long term field deployment in Massachusetts Bay, the controller housing and pump assembly are mounted about 2 meters above the ocean bottom within an instrumented tripod (Figure 9).
- The transmissometer is connected to the appropriate four-pin bulkhead connector on the WTS-Tr controller housing. The WTS is programmed with a pipeline file for a three to four month deployment using established field parameters for Massachusetts Bay (Appendix 1). This ensures that a copy of the diagnostic and deployment parameters is saved to a file for further review.
- Prior to deployment, each filter holder is fitted with an antifouling tip at its intake orifice. Each filter holder is also primed with filtered-distilled water to purge any air and connected to the pump assembly head. A saturated brine solution may be used for priming the filters and pump assembly system when sub-freezing air temperatures are anticipated during deployment operations.
- Upon recovery, the position of the valve on the pump head is noted (i.e. presumably at the home or number 1 position), the filter holders removed, and the plastic inserts installed in all the port couplings. Water remaining in each filter holder is drawn through the filter using low vacuum (10 mm Hg) from a vacuum pump. The unopened filter holders are then stored in a plastic bag and refrigerated until they can be analyzed in the laboratory.
- Access the WTS-Tr system by using a communication cable attached to the appropriate connectors of the controller housing and a laptop computer. Log on using the ProComm emulator program and the pump142 program along with an appropriate pipeline file. This will save all ensuing data to a file for further analysis.
- Access menu 2 (diagnostics) and allow the data to scroll through for about thirty seconds. This allows the user to review the current battery voltages of the WTS-Tr system.
- The recovery data is downloaded from menu 8 (offload data to a disc) and creating a file name with the extension .DAT to ensure proper display of data files on disc. After the data is offloaded, the PC will contain two files from the recovery of the instrument: a data file (.DAT) with only the data collected from the ocean bottom and the pipeline file which will contain the .DAT file as well as any other interactions with the software. This file can then be copied to disc and printed for review.