Hach 900 MAX Downlook Ultrasonic Sensor Troubleshooting, Appendix C, Problems, Causes, Solutions

Appendix C

Downlook Ultrasonic Sensor Troubleshooting

Problems	Causes	Solutions
		Wait a few minutes and see if the condition
RS485 Time Out—Did not get a	CPU is having trouble communicating	goes away. If it continues there amy be a
reading with the specified time	with the Ultrasonic board.	problem in the Ultrasonic, Velocity, or
allotted.		CPU board.
	Difficulty receiving a velocity reading.	Indicates an internal problem.
		Replace fuse. The fuse is located in position
Loss of Ultrasonic as Level	Blown fuse on CPU board.	F1 under the gray ribbon cable that connects
Measuring Device.		at position J1.
	Problem with the ultrasonic board.	Replace if necessary.
	Excessive foam on the water surface
	causes sound waves to be absorbed	Check for excessive foam.
	rather than reflected.
	Sensor is knicked or cut or improperly	Check for knicks, cuts, and the
	installed.	sensor installation.
U-Sonic Echo Loss—Flow Meter	Sensor must be level for proper return	Make sure the ultrasonic transducer is level.
	of signals.
Not Receiving a Return Echo
		Try shielding the transducer from convection
from the Ultrasonic Transducer.	Convection currents are present which
		currents. Echo loss should not exceed more
	varies the speed of sound.
		than two hours.
	Temperature calibration set up incorrectly.	Go through the temperature calibration
	Extreme high or low temperature	procedure and determine what the
	indicates a bad temperature transducer in	temperature the unit is sensing. Replace
	the temperature sensor.	transducer if necessary.
	Transducer is not connected.	Check the ultrasonic sensor connection on the
		flow meter.
U-Sonic Failure—No Signal from
	Cut or broken cable.	Check for any knick or cuts in the cable.
the Ultrasonic Transducer.
	Unusual temperature or inability to read	Re-calibrate the unit.
	new calibrated level.
	Liquid is too close to the transducer.	Try moving the transducer farther from the
		liquid.
	Obstructions under the transducer.	Check for obstructions on the front and sides
		of the transducer.
XDucer Ringing—False Return
		Clean the transducer face. If this is a constant
Echo mask Real Echoes.	Coating on the face of the transducer.	problem, try coating the face of the transducer
		with a very thin film of silicone grease to keep
		the debris from collecting.
	The transducer resonates against steel	Use the proper rubber isolation washers.
	mounting rails.
		Check the logged data to see when this
No Change in Level Readings or	—	started to occur. Go to the event log to see if
		anything happened during the same time.
Inaccurate Level Readings.
	Calibration	Re-calibrate the unit.
	Bad transducer.	Try a different transducer.

Page 130
Troubleshooting and Error Messages	8990apdx_tbl.fm