Adjusting Tank Monitor on an Audit 2U9

You may need to recalibrate your monitor if a sensor has been replaced. The sensors measure water pressure, and new sensors may have a slightly different voltage range, requiring the re-calibration procedure.

The system uses a solid state pressure sensor (Freescale Semiconductor MPXV5010GC6T1) connected to each tank near the bottom. The pressure measured is directly proportional to the height of liquid in the tank. The sensor has an accuracy and linearity of a small fraction of a percent. Essentially they are operated by connecting a voltage across 2 of the leads and the third lead outputs a voltage that varies from 0 to 7 volts depending on the pressure. Due to the height of the tanks, the usable output is 0V (empty) to ~4V(full).

• Empty all tanks.
• Turn monitor on and select holding tank screen.
• Locate connector pin #15 on the 24 pin connector.
• Momentarily short pin #15 to ground.
  • There should be a momentary switch for this located in front circuit breaker compartment, upper right corner.
• Center of screen should say “WAIT”..and then “DONE”
  • The computer now has those pressure readings (voltages) as empty readings.
• Fill all 3 tanks to fullest desired levels (yes all three (3), you can not calibrate just the single replaced sensor)
• Allow to settle for a minute, momentarily short pin #15 again to ground.
• The “WAIT” and “DONE” will appear, storing now the full voltage readings.
• Turn monitor off, wait 3 seconds, turn it back on and you are done.

Remove the dash panel by the entry door, the one with all the relays / breakers. There should be a momentary switch located in upper right facing forward or backward.

It may be visible or it may be just behind the panel about 4-5 inches inboard from the top right side of the board. Some coaches just have bare wires and no switch. The wires are normally both green, and shorting them together will pull pin #15 to ground.

Filling the fresh water tank is no different then what you normally do, plus you can see the level in the tank and stop it when its withing a few inches of the top.

Filling the black and grey tanks can be more of a chore, you can't see the level and filling them is not always easy. Here is a way to help.

This homemade manometer uses a sewer connection and garden hose to add water to the tank when the tank “dump” valve is open. It has a clear plastic tubing to read (see) the height of the water in the tanks. To get full status, all you do is watch the vertical clear tubing until the water reaches a height appropriate with being near the top of the tank. The PVC pipe is just there for support of the clear tubing, use what you like.