TIDE STATION USERS’ MANUAL Chapter 9 1

9Paroscientific pressure transducer

9.1Sensor description

The Paroscientific DigiQuartz high-accuracy pressure sensor is used in bubbler-based water level measurement systems. Bubbler-based systems determine depth of water by determining the amount of pressure required to force gas bubbles (air, nitrogen) through an orifice placed at some known distance above the bottom. National Ocean Service typically makes use of two orifices and two pressure transducers at a know spacing so that measurements can be corrected for water density. A typical DigiQuartz sensor is illustrated in Figure 11.1. Only the sensor is illustrated. A complete bubbler gage is composed of considerable additional equipment.

Figure 9. 1 ParoScientific DigiQuartz Pressure Sensor

9.2sensor installation

The DigiQuartz sensor(s) may be installed either external to the tide station enclosure or internally on the shelf. Follow installation procedures as recommended by the manufacturer of the bubbler gage system. Extend the serial interface cable from the sensor to RS-232 Termination Card number 2 inside the enclosure. If there is a second sensor you will need to add an additional RS-232 termination card and wire the card to an unused XPert port. Use one of the pre-punched holes in the lower left side of the enclosure to admit the serial cable. Seal around the cable with an appropriate packing gland or sealing material.

9.3sensor wiring

NOS standard wiring for the first DigiQuartz is to connect it to RS-232 Termination Card number 2, as illustrated in Figure 11.2. and Drawing 11.1

Figure 9. 2 RS-232 Termination Card #2

The DigiQuartz sensor must be connected to the RS-232 termination card by some type of adapter. The adapter must make the transition between the RS-232 DB-9 connector on the termination card and the DB-15 connector on the sensor. The adapter must provide power to the sensor, in addition to the necessary signal and ground. The DigiQuartz sensor is powered by voltages that can range between +5 and +20. The following table provides the correct wiring of the adapter.

DB-9 Connector / DB-15 Connector (sensor) / Function
Pin 2 / Pin 2 / TXD
Pin 3 / Pin 3 / RXD
Pin 5 / Pin 5 / Power and signal ground
Power supply wire + / Pin 9 / +12V power
Power suppy wire ground / Pin 5 / ground

Phil – Where should the +12V be obtained from??

9.4xpert software setup

9.4.1General Sensor Setup

A DigiQuartz sensor line file named ParoScientific DigiQuartz.ssf is included on the tide station CD. The file can be appended to an existing setup to incorporate the first DigiQuartz sensor. The file includes the proper setup for GOES data transmission. This file can be appended a second time and appropriate changes made to the block properties to incorporate a second sensor.

Figure 11.3 illustrates the ParoScientific DigiQuartz setup. The XPert contains a specific ParoScientific DigiQuartz block that opens the appropriate serial port and reads data from the sensor. For tide station applications the ParoScientific DigiQuartz block is sampled by a DQAP block that performs averaging according to the NOS standard. DQAP does a two-pass average in which the average is computed, outliers are removed (those values over 3 standard deviations from the computed mean), and the average is recomputed. The DQAP block provides four outputs. These outputs are the DQAP average, the standard deviation, the outlier count, and the sample count. The average, standard deviation, and outlier count are incorporated in the self-timed GOES transmissions.

Figure 9. 3 ParoScientific DigiQuartz Sensor Setup

9.4.2Specific Setup Properties

In general, you should not have to modify the properties provided in the setups on the tide station CD. If you do have to modify properties they will most likely be associated with the GOES data transmissions or the COM port assigned to the ParoScientific DigiQuartz sensor.

GOES transmission properties are set by editing the properties of the SelfTime block (icon) in the setup. These properties are illustrated in Figure 11.4.

Figure 9.4 GOES Self-timed Block Properties

The properties are all critical in some way. The label, for example, must match the label specified the NOS GOES format control table. (Refer to Appendix A.) If it does not, no data from the sensor will be transmitted. The data time and interval will almost never vary from the values shown. These are dictated by the NOS practice of using 3 or 6-minute averages collected every 6 minutes with the periods centered on the hour and 6 minute intervals thereafter.

The Num Values parameter determines how much information is available for incorporation in a GOES message. The value 30 indicates that the last 30 averages will be stored in the transmission buffer. Do NOT set this value too low. If you are asking for 10 averages per hour in a message plus two hours of redundant data you will need at least 30 for Num Values. Any less will result in a loss of redundant data. Station using the newer 6-minute transmission intervals will not require a value greater than two (2) for Num Values.

The COM port assignment for the ParoScientific DigiQuartz sensor is set by editing the properties of the ParoScientific DigiQuartz block, as illustrated in Figure 9.5.

Figure 9. 5 ParoScientific DigiQuartz Air Gap Sensor Block Properties

9.4.3NOSGOESFormat.txt File

If you are using the NOS GOES data transmission format you will have to add a line to the NOSGOESFormat.txt file. An appropriate line is contained on the example CD as Miros Air Gap.txt Here is the contents of the file. Refer to Appendix A for a complete explanation of the line contents. Be sure to change the sequence number (first character on the line – shown here as 0) if you want the Air Gap values included in a dial-in report.

1,Miros Air Gap,x,!,AIRGAP,10,3,MSO,STD,OUT (flag for ParoScientific DigiQuartz is unknown)

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