Testing Temperature and Level Sensors

The Test Temperature & Level selection on the Manual menu is used primarily by the Milnor® factory for testing and calibration of machines before delivery. For testing a temperature or level sensor in the field, the input to the sensor (level or temperature) must be controlled, but the sensor must remain connected to the processor board. The temperature sensor can be tested with a container of ice and water. A probe inserted in a container filled with ice and water will register approximately 32 degrees Fahrenheit (0 degrees Celsius).

 

Viewing Water Level Data During Operation

Display or Action	Explanation
	This key sequence displays pressure transducer raw data and actual water level in tenths from left to right, the bottom line displays the pressure transducer raw data, the actual water level and the filtered water level in tenths, and the desired level.
	This key sequence displays the calculated level, the desired level, and the temperature from left to right, the bottom line displays the calculate water level, the desired water level, and the water temperature. The level values on this display take into account any configured offset height.

Display or Action

Explanation

The top line of the display applies to the level sensing circuit. The “R” and the five characters immediately following it on the top line indicate the voltage being delivered by the pressure transducer on the processor board. The “A” value is the actual instantaneous level read by the transducer. Because this display is only available when the drain is open, the actual level will normally reflect no water in the machine cylinder, although the number will be above 0. The “C” value is a calculated average of the transducer levels, used to negate the effects of rising and falling water levels caused by the reversing wash motion. Again, in normal conditions, this value will reflect that there is no water in the machine, although it may fluctuate between two values (e.g., 1.0 and 2.0) as it adjusts to the nearest whole inch. The bottom line of the display applies to the temperature sensing circuit. Similar to the “R” value of the top line, the first six characters of the bottom line indicate the voltage being delivered by the temperature probe to the processor board (see Figure 7). The “A” value on the bottom line is the temperature in degrees Fahrenheit detected by the temperature probe.

 

Testing the Pressure Transducer Circuit

First lets get a gauge of what data is being interpreted. We want to run a formula that is essentially a standing bath, no basket rotation, and a typical water level. At any point during formula, press the three right buttons on the controller; this displays the raw counts. A picture of this data will help in the troubleshooting process, remember roughly how much water is in the machine when this picture is taken.

The pressure transducer, illustrated in the picture below, outputs a microvolt-level signal that increases proportionally according to the pressure in the plastic tube. The instrumentation amplifier has a signal gain 1000 / 500 for the microprocessor. Because only very sensitive voltmeters are capable of reading a signal of less than one millivolt, better results are available by measuring the output voltage from the instrumentation amplifier. This procedure is described below:

1. Locate the instrumentation amplifier on the processor board. This is a small integrated circuit chip with eight leads in socket IC20, near the pressure transducer.
2. Set your digital voltmeter to read a maximum of 5 volts DC. The output of this component, even when failed, will not exceed 5 VDC.
3. Locate pin 6 on the instrumentation amplifier. Note the notch in one end of the amplifier chip. If the board is oriented so the notch on the chip is at the left side of the chip, then pin 1 is the leftmost pin on the bottom row. Count pins counterclockwise to pin 6. If the orientation of the board is maintained (pin 1 at the lower left), then pin 6 will be the second chip from the right on the top row. This is the amplifier output pin.
4. Put the positive lead from your voltmeter on pin 6 of the amplifier chip, and the negative lead to a reliable electronic ground. Pin 5 (rightmost pin on top row) of the amplifier chip provides a suitable ground.

The output voltage read on the meter should be approximately 0.085 volts per inch of water in the machine cylinder. That is, if the machine is filled to a level of 4 inches (10 cm), the voltage measured between pins 5 and 6 of a functioning amplifier will be about 0.33 volts.

WUV7J1B ####H - High Gain software (1000 gain)
WUV7J1BA ####J - Low Gain software (500 gain)

Engineering behind the scenes:

Some chemical folks like extreme levels, and we would argue that this is not needed and just wastes water. Each processor board has a maximum absolute level: 17, 20 and 22 inches (refer to table below). The maximum absolute levels are calculated from the formula below. Sample value of 14in desired and 40 offset has been added. Note, this sample would cause the 08BH188AT Rev H board to continue to fill forever.
 

Boards and technical data

Board	Revision	Max Level	IC20 Chip
08BH188EPxx	ALL	20 in.	Socket
08BH188xx	ALL except Rev H.	20 in.	Socket
08BH188AT	H	17 in.	Soldered
08BH188BT	J & K	22 in.	Soldered

If your chemical company is still pushing for a higher level, update the board to the latest revision of 08BH188BT and the latest revision of WUV7J1BA.
Under no circumstances should absolute level exceed 22 inches.