168Service Manual – SC5000 30 - Solution System
The senor’s internal circuitry consumes only about 30 µA (10 µA per
sensor body), but when the 2k Ω resistor is added, the consumption
jumps to approximately 2.5 mA per sensor body. This amperage is
cumulative, such that as each sensor body detects capacitance, the
total consumed amperage increases approximately 2.5 mA each.
Operation at the MMC
The operation of the solution level sensor poses a unique situation
for the Main Machine Controller, because it is a 2-wire device with 4
unique states. Therefore, the controller needs to provide power to the
sensor, and monitor how much amperage is being consumed.
The most common method for an electrical system to monitor
amperage, is to send the current through a known but small resistor to
ground, and then measuring the voltage drop across that resistor and
sending that signal to an analog-to-digital converter. In this case, the
known resistor is 100 Ω.
Currently, the Service Menu is displaying the voltage drop across
the resistor, instead of the amperage through it, but the only
difference is a decimal point position. The table below summarizes
the predicted versus actual values from an actual machine.
Note: The difference between predicted and actual values listed
below is due to minor variations in such small resistance values. For this particular machine, the sensor’s
switching resistors were 2088 Ω, instead of 2000 Ω, and the MMC’s sinking resistor was 101 Ω instead of
100 Ω.
Sensor
Level
Predicted
Amperage
Actual
Amperage
Displayed
Voltage
None 0.03 mA 0.03 mA 0.00 V
1 Sensor 2.50 mA 2.39 mA 0.24 V
2 Sensors 5.00 mA 4.51 mA 0.44 V
3 Sensors 7.50 mA 6.44 mA 0.64 V
External Wash Options
The wash hose option and the scrub-n-vac option each use an on-demand uid pump at the rear of the
machine to drive pressurized water to the exible wash hose. The pump itself monitors the output for uid
ow by pressure drop, and activates when the operator uses water. The inlet to this pump is in the solution
hose, but upstream from the solution solenoid. A machine can use only one option or the other, but not both.
2k Ω
2k Ω
2k Ω
100 Ω
MMC Actual
.25 V = 2.5 mA
+5V
Gnd
MMC
Amps
A
Volts
V
A1 Main Controller
J2-3 SOLUTION LEVEL
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J1-14 SOLUTION SOL
M24 DETERGENT PUMP
0.44
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