Luminometer General Information

The following drive mechanisms perform the mechanical functions of the Luminometer:

• Transport drive mechanism —positions the MTU inside the Luminometer.
• Door/shutter drive—controls the movement of the door and the shutter, and engages the transport hook and isolator because they are connected to the movement of the door and shutter, respectively.

Transport Drive

Transport drive mechanism uses a stepper motor connected directly to a pulley and belt system that moves a hook along a sliding linear bearing. The hook engages the upper notch on the end of the MTU opposite the barcode. The hook positions the MTU inside the Luminometer from the home position, where it is deposited by the Distributor to each of the five reading positions where the MTU tubes are in front of the PMT. Transport drive returns MTU to the home position at the end of the process where it can be retrieved by the Distributor. The entire transport assembly can rotate around the motor axis so that it can engage and disengage the hook into the MTU. The rotation of the transport is controlled by the door/shutter drive as explained below.

Door/Shutter Drive

The door/shutter drive mechanism uses a stepper motor that drives both the door and the shutter via cams, which allows the door to open and close during one half of the drive intended travel and the shutter to open and close during the other half. The stepper motor has shafts on both ends that are attached to drive arms. Each drive arm has a pin with a plain bearing that engages a slot in a plate. One plate is connected to the door, the other to the shutter. The slots act as cams and each has a curved section and a straight section. While in the straight section, drive arm will move the connected component (door or shutter). While in the curved section the connected component does not move. This is what allows the drive to move only the door during part of the range and only the shutter during the other part of the range. Also, this drive system will not allow the door and shutter to be open at the same time.

Shutter/Isolator

The shutter has an integrated isolator. It is essentially a sliding plate with a cylindrical feature on the front that slides over the MTU tube that is positioned for a light-off reading. There is a rectangular "window" feature that allows the PMT visibility into the cylindrical isolator feature where the tube resides while the shutter is in the open (isolator engaged) position.

Door

Luminometer door is a sliding plate housed in the front part of the Luminometer. The door simply slides from the opened position to the closed position while an MTU is inside the Luminometer to prevent ambient light from entering. The door has a tab with a pin and plain bearing that engage a slot on the end of the transport drive mechanism. As the door moves from opened to closed it also rotates the transport drive mechanism so that the hook engages the MTU. When the door opens, the MTU hook disengages the MTU.

Three slotted optical switches (sensors) verify mechanical functions in the Luminometer. Thin metal tabs ("flags") are part of the door, hook, and shutter drive arm. These flags break the optical path between a switch's emitter and sensor, which changes the switch's state.

Transport Home Sensor

The transport has six positions during normal operation. They are the home position and positions one through five corresponding to the position of each of the five MTU tubes while directly in front of the PMT. The optical switch on the transport drive is located such that the hook flag enters the switch slot when it is in the home position. The home position is the position in which the hook must be while engaging an MTU deposited into the Luminometer by the Distributor. During a reset the transport drive slowly moves into the home switch to establish its home position. The drive moves the hook to each tube reading position by driving the stepper motor a certain number of steps. After a move to one of the reading positions the drive moves the hook to the home position before moving to another reading position. This allows the control to determine if the motor has moved the drive correctly. If the home switch changes states too soon, too late, or not at all then the transport has failed to move correctly.

Door/Shutter Sensors

There are three positions of the door/shutter drive during normal operation but only two optical switches. The positions are "door open", "door closed", and "shutter open". They are sequential as the drive motor rotates such that "shutter open" cannot be reached from "door open" without going through the "door closed" position and vice versa. Optical switches only change state at the "door open" and "shutter open" position. Movement errors of this drive can be determined based on when the optical switches change state relative to the number of steps the motor has been driven at the time of the state change. Because the positions are sequential, an error during a "door closed" move will be detected on the subsequent move.

• Door open is the home position and is the position where the door flag causes the door's optical switch to change state. While the door is open the transport drive is rotated such that the hook is in the disengaged position (described above). The shutter is closed while the door is open.
• Door closed is the next position. When the door closes the transport drive rotates so that the hook is in the engaged position. The shutter remains closed in the door closed position. There is not an optical switch that changes state when the drive is in this position.
• Shutter open is the last position, where the PMT has visibility through the window in the shutter/isolator to the MTU tube and the cylindrical feature of the shutter/isolator is a around the tube. At this position, the flag on the shutter drive arm causes the shutter switch to change state. The door remains closed while in the "shutter open" position.

Luminometer uses an optical sensor to verify that AD1 and AD2 are dispensed correctly.

Sensor assembly is installed in the top part of the Luminometer housing. The injector passes through an opening in the sensor assembly. Sensor assembly consists of two sensors and two emitters attached to a small PCB. Injector assembly tubing extends down into the injector. Injector contains four small windows through which infrared (IR) light passes.

IR light generated by emitter passes through one window, injector tubing and out the opposite window to the sensor. Amount of IR light that passes through injector varies with the presence of liquid in the tubing.

Prior to an injection, the fluid in the injector tubing will not extend down to the area adjacent to the dispense verification sensor. After the dispense, a pullback occurs where LCMPs briefly pump in the opposite direction so that the fluid in the tube is pulled up again above the sensor level. This functionality allows dispense verification. Sensor signal contains three distinct time regions: initial air (from the previous pullback), liquid dispense, and final air pullback.

Signal is analyzed in each region to determine if the signal substantially matches the expected air/liquid signal. Small signal discrepancies are allowed, but larger discrepancies will generate an error. The specific region parameters and the acquired sensor signal for each dispense are logged in the ProcessControlData_luminometer.curve file.

Air/liquid threshold value is determined by sensor calibration that is performed as part of the system Full PrimeOperation of pumping fluid through tubing to ensure proper and consistent fluid delivery (remove air from the tubing, etc.). routine.

OLV (Optical Level Verification) system incorporates a liquid/air sensor near the injector orifice. Each dispense is followed by an airgap pullback. This pulls air back up past the sensor after each dispense. Therefore, the subsequent dispense starts with air in the tubing in front of the sensor.

The sensor signal for a good dispense is composed of the following phases:

1. Process starts a high signal (indicating air).
2. Signal transitions to a low signal (indicating liquid) as fluid is dispensed.
3. Signal remains low (indicating liquid) as the pullback begins.
4. Signal finally transitions to a high signal (air) as the air/liquid interface is drawn up past the sensor.

It is important that the sight holes in the injector body remain free from debris, fluid, and dried salt solutions, as any visual obstruction in these holes will result in erroneous failure flags.

The algorithm splits the air-liquid-air signal into four distinct regions. These regions are each defined by the following parameters:

• Start point
• End point
• Criteria (air or liquid)
• Minimum number of points required to meet the criteria

Threshold defined during sensor calibration, as part of a Full Prime procedure, is used to determine if each data point is considered as air or liquid. Threshold calculation sets the threshold at 1/3.5 (which is 28%) of the way from the liquid value to the air value.

For a dispense to be considered good, the following conditions must be met:

• Region 1 check passes (this is the initial air check)
• Region 2 check passes (this is the liquid phase check)
• Region 3 and/or 4 passes (this is the final air pullback check)

If Region 3 fails, then Region 1 is ignored on the subsequent dispense. This is to eliminate a false failure mode where the air/fluid interface does not pullback cleanly and instead leaves droplets on the inside of the tubing in front of the sensor.

Specific region parameters and acquired sensor signal for each dispense are logged in the ProcessControlData_luminometer.curve file. Sensor ID 0 corresponds to AD1 and Sensor ID 1 corresponds to AD2.

Typically, process control system will generate failure flags when the system is dispensing air instead of liquid. This may be observed in the curve file data as Region 2 failures. In this case, the system should be inspected for the following conditions:

• An empty AD1 or AD2 bottle
• A disconnected AD1 or AD2 bottle
• A loose fitting in the fluid line from the bottles to the injector
• A damaged fitting or tubing in the fluid line from the bottle to the injector
• Air or occlusion in fluid line from the bottles to the injector
• A Leaky AD1 or AD2 pump

If injector is actually dispensing properly then failure is a false flag due to a problem with the process control system. In such case the system should be inspected for the following:

• Wet or damaged process control PCB in the Luminometer lid
• Damaged or unplugged process control cable in the luminometer (from the main PCB to the process control PCB)
• Debris or liquid in the sight holes of the injector
• Defective luminometer injector housing tubing (defective injector)

If system has a Luminometer process control system failure, this failure can be confirmed by performing a Full Prime because the process control system is calibrated during a Full Prime and is used to check to be sure that the bottles are correctly connected during a Full Prime. The process control system is not exercised during a Mini Prime.