Appendix III. Analogue Recorders

Appendix III-1. Type F Water Level Recorder

a) Description

The Type F recorder is a horizontal drum type, with unrestricted drum rotation. The service interval for the Type F is limited to 7- or 28-day periods, depending on the gearing.

Unless retrofitted with a data logger add-on (Figure III-1), the Type F recorder is not recommended for general use in natural stream channels because it is difficult to extract hourly water level values during periods of significant change in stage. However, because the various water management agencies in BC own many Type F recorders, limited use of this existing equipment may be justified economically, e.g., to provide a record of stage at lakes or reservoirs, or to provide a record of flow rates, for licensing purposes, below diversion structures in rated channels designed to transport water at a near-constant rate.

Figure III-1. Stevens Type F Recorder

Note: Type F recorders are fitted with electronic (DC), electric (AC), mechanically driven double spring 8-day or weight-driven clocks. The latter require a 5.44-kg weight in direct drive; this weight will travel 0.415 m over a 7-day period.

b) Installation

These instructions refer to installing existing recorders, i.e. those currently in the possession of an agency, not to new ones.

1. Bench check recorder. Obtain a copy of manufacturer's operating manual and spare parts list.
2. Endure all parts are in place and tested.
3. Check the condition of the braided copper wire that controls the lateral movement of the stylus carriage.
4. If the stylus is of the ink reservoir type, order a felt pen adapter and a supply of cartridges.
5. Check the gear that controls movement between the float line pulley and the chart drum. Normally the movement will be a 5:1 ratio, although finer definition may be desirable for some applications.
6. Remove and service the clock (see servicing clocks, Appendix III-3).
7. If clock drive is weight driven mechanical, examine the weight suspension wire and sprung weight attachment clamp.
8. Check the condition of the float, ensure the float suspension cable or tape is of sufficient length for the proposed location and that the counterweight matches the float size.
9. Order a supply of chart sheets, pen cartridges, and any replacement parts.
10. Bench test the recorder for several days on completion of maintenance. Observe clock accuracy and adjust as necessary. See section on clocks, part c of Appendix III-2.

Note: There is a minimum internal diameter for the stilling well to provide clearance for the suspended float, counterweight, and clock weight. If a mechanical weight-driven clock is to be used, the recorder shelter floor should be placed at least 75 cm above the highest expected water level. If the weight becomes submerged, the effective weight is reduced and so is the accuracy of the clock regulator. (Stilling Wells, Instrument Shelters, and Float Sizes are discussed in Section C.2 and C.3.)

c) Data Logger Add-on

Type F graphic data recorders can be "converted" to produce electronic data by adding on a digital data logger. With the digital data logger add-on, the Type F becomes suitable for where longer term data retrieval service visits are desirable. The chart record is not improved in any way; however, the digital data logger will provide the necessary time/water level definition.

Note: The constraints in the use of horizontal drum recorders indicated above do not apply to the European designed models in which the time base is drum rotation and the water level is recorded cross the length of the drum. Some models are fitted with a reverse recording mechanism offering unlimited stage range. The commonly used time scale, 2 mm per hour, requires servicing every 8 days.