Agitator: The optional agitator is a device which screws on to the sensor and causes water to flow
past the tip at the proper rate. It stays with the sensor to continuously ensure accurate results. The
unit is pressure-proofed for operation to 150 ft. depths.
Fast moving water: When analyzing fast moving water from rivers, streams, pipes, or conduits
the water flow may be sufficient for accurate reading. Face the membrane tip of the sensor directly
into the flow.
Make sure that at least one inch of the sensor tip is completely and continually
submerged. The flow should be at least 1 ft. per second. Water flow is sufficient if swishing the
sensor rapidly in the water does not cause the readings to move upscale further.
Prior to sensor and electronic circuit adjustment, please take time to read this brief circuit description.
The Model 924 analyzer electronic circuitry consists of: (See Block Diagram Fig. 1)
MOTHERBOARD Fig. 9
The Motherboard provides interconnections between the input connector board, the power supply board, the
several option boards, and the processor/display board. In drawing 30998 the various input and output signals
are identified by number.
POWER SUPPLY BOARD Fig. 10
The power supply employs linear regulators to provide plus and minus 15 volts and a switching regulator to
supply up to one ampere at five volts. The transformer has a dual primary which may be jumpered for 110 or
220 volt ac lines. The transformer secondary used to supply ac to the minus 15-volt regulator also supplies 18
VAC to the current output board.
PROCESSOR/DISPLAY BOARD Fig. 11
The processor/display board is mounted on hinged stand-offs to allow access to the other circuit boards. When
the instrument is turned on, it initiates a series of self-checks.
The ROM is summed and the result compared to a stored checksum. If this comparison fails, it means
the ROM contents have changed and the ROM is unusable. In case of checksum failure the error
message H001 is displayed, and the program is restarted.
All locations of RAM are given a read/write check to insure that all locations may be written and read,
and that writing affects only the location being written. Failure means the instrument is inoperable. In
case of RAM failure the error message H003 is displayed, and the program is restarted.