Field Calibration Procedure

This instrument is battery powered; therefore, it is highly recommended that a fresh set of 9 volt alkaline batteries be used to operate the unit during calibration. The calibration of this instrument will remain accurate throughout the aging cycle of the batteries due to an onboard voltage regulator circuit. Additionally, the display will turn off and the "low battery" indictor will light before the accuracy is affected by a failing battery. Nevertheless, fresh batteries are recommended during calibration. It is not necessary to calibrate the instrument each time batteries are replaced.

Be aware that when field calibrating the 48A, you are also compensating for variations in the pressure and temperature sensors. The Sensor Package which is attached to the main body of the vessel is NOT adjustable, and no attempt should be made to open the package or alter its function. All calibration adjustments are inside the Model 48A Volume Computer. Once the calibration has been performed, it is imperative that the 48A Computer and Sensor Package Vessel remain a matched pair Serial numbers can be found on the back of the Volume Computer and directly below the transducer cover (12059). The units are sold as matched pairs from the factory. If a Volume Computer or vessel is mis-matched, then the calibration procedure will have to be repeated.

Preparation:

1. Remove the four rubber feet on the back of the computer, exposing the four screws which hold the unit together.

2. Remove the four screws using a No. 1 Phillips screwdriver.

3. Unplug the top half from the bottom half of the unit by pulling firmly and evenly on both halves.

4. Connect the two printed circuit boards together using a 24-circuit boards together using a 24-circuit male to female jumper (12015).

5. Position the assembly so the display is visible and the trimpots on the Processor Board are accessible. It is not necessary (or recommended) to remove either printed circuit board from its mounting.

6. Connect the Vessel Sensor Package assembly to the Volume Computer using the cable supplied.

Adjustment to the Internal Voltage Reference:

Note: This adjustment requires a 3-1/2 digit digital voltmeter. If one is not available, skip this part of the procedure and go on to Temperature Calibration.

1. Connect the minus lead of the DVM to ground (see Fig.1).

2. Connect the plus lead of the DVM to TP-1 at lower end of 10K resistor ( see Fig. 1.) Figure 1

3. Turn the Volume Computer on by pressing the PRESS mode switch.

4. Adjust the REF trimpot for a reading of exactly +1.920 volts.

Temperature Calibration:

Note: A controlled temperature chamber equipped with a calibrated laboratory thermometer or temperature monitoring system is required for this adjustment. The usable temperature range of the Series 12,000 Volume Computer is from +26.0 degrees F. To +57.0 degrees F. Therefore, the test temperatures must be within this range. At all times, the Volume Computer itself should be kept at room temperature. Only the vessel assembly (sensor package) need to be located inside the temperature chamber.

To Calibrate:

1. Place the vessel in the temperature chamber and run the temperature down to +28F.

2. Allow the assembly to stabilize at this temperature for at least 20 minutes.

3. Press the TEMP mode switch on the Volume Computer and check the reading. If it is not the same as the reference thermometer, adjust the SPAN trimpot for the correct reading.

4. Run the temperature chamber up to +55 F.

5. Allow the assembly to stabilize for at least 20 minutes.

6. Press the TEMP.. mode switch on the Volume Computer and check the reading. It if is not the same as the reference thermometer, adjust the ZERO trimpot for the correct reading.

7. These two adjustments are slightly interactive; therefore, it is necessary to repeat the procedure (steps 1 through 6 above) until no further correction is required.

Pressure Calibration:

Note; Pressure calibration requires a compressed air (or pressurized liquid) source which is equipped with a highly accurate readout system, accurate and readable to +.1 lb.

1. Apply 0.5 psi pressure to the sensor vessel (Go in through either valved port. Use the other for bleeding).

2. Select the PRESS mode on the Volume Computer.

3. Check the reading. If it does not match the applied pressure, adjust the NULL trimpot for the correct reading.

4. Increase the pressure to 24 psi.

5. Check the reading. If it does not match the applied pressure, adjust the GAIN trimpot for the correct reading.

6. Bleed the pressure down to 0.5 psi and re-check the reading. A few cycles may be required as the adjustments are slightly interactive.

Re-assemble the Volume Computer in reverse sequence from that called out in the preparation section. Exercise care not to disturb the trimpot settings.

Care of the Instrument:

A) After the test has been completed open both inlet and outlet valves (12020-B) and blow out the beer sample with pressure from the aspirator bulb (12042).

B) Rinse the inside of the Volume Meter with water to remove any traces of beer. This can be accomplished by attaching a hose from a water source to the gooseneck (12045) and then opening the inlet and outlet valves to let water flush through the instrument. Do not use hot water as it will damage the thermometer.

C. Apply a small amount of "O" ring lubricant to the piston (12005) and work the piston up and down to lubricate the internal piston "O" ring (12009).

D. Rinse out any traces of beer from the aspirator bulb (12042) to prevent the check valve from sticking.

E. If the computer becomes soiled, clean the case with a soft damp cloth and dry. Do not submerge the computer in water.