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15
SHOP CALIBRATION
 
A. TEST AND CALIBRATION IN SHOP
 
15A1. General. When it becomes necessary to remove the main balance arm, auxiliary balance arm, main force arm, or the A-spring from the instrument, the procedure generally followed is to remove the instrument from the ship and overhaul it on a tender or in a shop. The most practical means of checking the instruments before installation in the ship is to operate them in the shop under the same conditions as encountered in service. After overhaul, the cam and pointer should be adjusted to the zero position (see Section 15A6), and the instrument should be balanced (see Section 15A7), and calibrated in the shop. The bellows should be tested, if necessary, under water pressure of 300 psi.

15A2. Equipment required. (See Figure 151.) The equipment described below is the minimum required for properly testing the Bendix log. It an be assembled and installed at a tender or base shop from readily available material. The following hydraulic equipment is necessary: a water storage tank, or water line with connection, static pressure tank, dynamic pressure tank, pressure storage tank, pressure gage, air compressor, water level gages, knot scale, hydraulic hose, and fittings and connections. This equipment is described in the following paragraphs.

15A3. Knot scale. (See Figure 15-1.) The knot scale is laid off from the values listed below, and is preferably made of metal. The lines are cut with a milling machine or jig borer, so that the distances from the zero line can be accurately measured. This scale is suitable for use only with fresh water in tanks and system, and is designed for calibrating Bendix log instruments only. Pressure values from rodmeters of other manufacturers may differ from the pressure values indicated here, probably necessitating the use of a different scale. However, with a correct scale, this equipment may be used on other types of logs operating on the principle of pressure differences from a rodmeter. The scale should

  be mounted so that it can be shifted upward and downward approximately 6 inches, or else the left-hand static tank must be movable. The distances to be marked above zero, corresponding to knots are listed as follows:

KnotsDistance (in.)
above zero
10.543
22.170
34.879
48.674
513.553
619.516
725.383
834.696
943.912
1054.212

15A4. Pressure tanks. (See Figure 15-1.) Two pressure tanks are mounted, one on each side of the knot scale. The tank on the right side supplies dynamic water pressure. The left-hand tank supplies static water pressure. Provision is made for raising and lowering the right-hand (dynamic tank, while the left-hand (static) tank is stationary, unless the scale is stationary, in which case the latter tank must be movable, too. When the dynamic tank is elevated above the static tank, the head, or difference of level of water, creates a pressure difference which is equal to the dynamic pressure at some known speed. Water level gages are mounted in front of the pressure tanks and show the exact level of water in each tank. The knot scale mounted between these pressure tanks is calibrated in knots and enables the water level to be read closely, even at low speeds. The tanks are made of 3- or 4-inch heavy-duty pipe, preferably brass, approximately 18 inches long, with heavy threaded caps at each end. The glass tubing and gage fittings should, be able to withstand a pressure of 400 psi for safety. Shut-off cocks should be mounted on the lower ends, ahead of the nipples. Shutoff

 
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Figure 15-1. Shop calibration equipment.
1. WATER STORAGE TANK
2. KNOT SCALE
3. STATIC PRESSURE TANK
4. WATER LEVEL GAGES
5. SPEED AND DISTANCE INDICATOR
6. MASTER TRANSMITTER INDICATOR
7. STATIC HOSE
8. AIR COMPRESSOR LINE (OPTIONAL)
9. DYNAMIC PRESSURE TANK
10. COUNTERWEIGHT
11. AIR LINE TO STATIC PRESSURE TANK
12. PRESSURE GAGE
13. PRESSURE STORAGE TANK
14. VENT LINE
15. HAND PUMP PRESSURE LINE

Figure 15-1. Shop calibration equipment.
 
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Figure 15-2. Cam positioned prior to setting pointer to exact zero.
1. SPEED TRANSMITTER DRIVEN GEAR
2. POINTER HUB
3. CAM BRACKET
4. SPEED TRANSMITTER DRIVE GEAR
5. CAM
6. CAM FOLLOWER (BEARING)
7. MAIN FORCE ARM EXTENSION

Figure 15-2. Cam positioned prior to setting pointer to exact zero.
 
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cocks are not required at the top. When mounted as shown in Figure 15-1, the left-hand (static) tank is connected to the static line. The right-hand (dynamic) tank is suspended on a chain, or cord, which is connected to a counterweight so that it may be moved upward or downward as desired. The tanks should be mounted so that the zero   water level is at least 4 feet above the bellows. However, the shop ceiling may be a determining factor, and may not permit raising the dynamic tank to the 10-knot mark on the scale. In this case the distance of the zero water level above the bellows will have to be less than 4 feet.
Figure 15-3. Balancing master transmitter indicator, Step 1.
1. "A1" ADJUSTMENT KNOB
2. "A" ADJUSTMENT ASSEMBLY ATTACHED TO MAIN BALANCE ARM
3. "A2" RING TURNED ALL WAY DOWN
4. REFERENCE MARKS
5. REFERENCE POST
6. CONTACT ARM
7. CONTACT ADJUSTING SCREWS
8. "B" SPRING ASSEMBLY REMOVED
9. MAIN BALANCE ARM ADJUSTING SCREWS
10. CONTACT LOCK SCREWS
11. MAIN BALANCE ARM COUNTERWEIGHT REMOVED

Figure 15-3. Balancing master transmitter indicator, Step 1.
 
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Figure 15-4. Balancing master transmitter indicator, Step 2.
1. STRING
2. A ADJUSTMENT, ASSEMBLY
3. CONNECTOR SCREW CONNECTION
4. B SPRING
5. CONTACT ARM
6. AUXILIARY BALANCE ARM
7. MAIN BALANCE ARM
8. MAIN FORCE ARM
9. CONNECTOR SCREW
Figure 15-4. Balancing master transmitter indicator, Step 2.

15A5. Water and air connections. (Figure 15-1.) The hose connecting the dynamic tank to the lower fitting of the bellows must be long enough to permit the dynamic tank to be raised to the extreme upper position of 10 knots. The nipples on the upper ends of the tanks are connected together, and the hoses are so arranged that they can be connected to either a water supply, or to a water storage tank, mounted from 8 to 12 feet above the tanks; and to an air pressure line capable of delivering a pressure of at least 100 psi. A pressure storage tank mounted as shown in the illustration permits the use of higher

  pressures which are developed in the top of the tank when water is pumped up into it from below by a hand pump. An air-pressure gage should be mounted on either the dynamic or static tanks, on the common air line, or on the pressure storage tank. Connect the upper bellows fitting to the static tank.

15A6. Aligning cam and pointer to exact zero position. (See Figure 15-2.) Remove the pointer and dial before calibrating the log; align the cam and pointer to the exact zero position as follows: Manually turn the driven gear on the power motor drive gear assembly until the bearing (follower) on the main force arm extension falls into the groove provided in the cam as shown in the illustration. Install the dial and pointer with the pointer set at zero position on the dial. Manually turn the power motor-driven gear until the pointer registers 1.2 knots on the dial. This is the exact zero setting of the pointer and cam. Loosen the pointer screw and move the pointer back to zero position on the dial. Tighten the pointer screw and pin the pointer to the pointer hub.

15A7. Balancing master transmitter indicator. (See Figures 15-3, 15-4, and 15-5.)

a. Whenever the A-adjustment assembly is replaced, or whenever the arms are removed, it is necessary to balance the log mechanism before calibration. The first steps in balancing the master transmitter indicator are accomplished as follows: Remove the counterweight from the bottom of the main balance arm by removing the screw and lock washer that secure the counterweight to the arm. Turn the A2-adjustment ring in a clockwise direction as far as possible. This will stretch the A-spring. Remove the B-spring by unscrewing the B-spring connector screw from the rocker on the top right side of the main balance arm. Energize the power motor. Position the contact block so that the contact arm is in a neutral position when the pointer reads zero by loosening the two lock screws at the bottom of the contact block, and then turning the contact block adjusting screws until the contact arm is positioned in a neutral position. Align the

 
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Figure 15-5. Contact arm and contacts installed.
1. PIVOT SCREW
2. CONTACT ARM SUPPORT
3. HIGH-SPEED REVERSE CONTACT
4. CONTACT ARM
5. TERMINAL
6. CONTACT ARM CONTACT
7. PIGTAIL
8. SLOW-SPEED REVERSE CONTACT
9. HIGH-SPEED FORWARD CONTACT
10. SLOWSPEED FORWARD CONTACT
11. CONTACT ADJUSTING SCREWS
12. CONTACT LOCK SCREWS

Figure 15-5. Contact arm and contacts installed.
reference marks on the reference post and on the main balance arm by loosening the lock nut on the rear of the main mounting plate and turning the reference post until the reference marks are aligned (Figure 15-3). Deenergize the power motor. Turn the main balance arm adjusting screws on the main force bearing so that the contact arm will move through an are sufficient to position the arm contact on the exact center of each high-speed contact, then   tighten the lock nut on each adjusting screw.

b. The second step in balancing the master transmitter indicator is accomplished as follows: Disconnect the connector screw on the A-spring from the rocker on the left side of the main balance arm. Tilt the A-adjustment assembly to a horizontal position, and tie it in this position so that it will clear the rest of the mechanism as shown in Figure 15-4. Place the B-spring in the spring

 
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force hub at the top of the auxiliary balance arm, and install the B-spring connector screw that secures the spring to the rocker in the right side of the main balance arm. Install the adjusting nut and thin lock nut at the top of the B-spring so that there is no tension and no slack in the B-spring. Install the counterweight on the bottom of the main balance arm and secure it with a screw and lock washer. Shift the position of the counterweight on the main balance arm until the reference mark on the reference post is aligned with the reference mark on the main balance arm (Figure 15-3) when the arm is freely balanced. When the reference marks are aligned, pin the main balance counterweight in position. It is not always possible to pin through the old pin hole. In such cases, a new hole should be drilled and a pin installed through it. Be careful not to get chips in any part of the instrument. Remove the string from the A-adjustment assembly and connect the A-adjustment assembly connector screw to the rocker at the left side of the main balance arm. Tighten the connector screw.

15A8. Preparing shop equipment prior to testing. Fill both the static and dynamic pressure tanks nearly to the top with fresh water and vent the hydraulic system as described in Section 11A5.

15A9. Testing equipment at surface pressure. (See Figures 7-2 and 7-3.) To operate the unit at normal surface pressure, set the valves of the bellows to the operating position. Vent both the static and dynamic tanks to the same level at the zero point on the knot scale. The top connections of the tanks are open to the atmosphere. Energize the master transmitter indicator. Set the instrument to zero by means of the C-adjustment as described in Section 13A4. Raise the dynamic pressure tank to the desired knot mark on the scale as illustrated in Figure 7-3. If adjusted properly, the pointer of the master transmitter indicator will indicate the same speed. Lowering the dynamic tank to the zero mark as shown in Figure 7-2 should

  cause the master unit to return to a zero indication of the pointer.

15A10. Testing equipment (submerged condition). Connect the common pressure hose at the top of the tanks to a controllable supply of air, preferably from the pressure storage tank. Apply air slowly, and test at steps of 50 psi. Because of hose expansion with pressure increase, the water level in the tanks may change and the zero of the scale may have to be lowered slightly. Pressure beyond 200 psi is not necessary if the parts operate satisfactorily up to this pressure. No part of the bellows assembly should leak. If the test under pressure (submerged condition) is satisfactory, release the air pressure from the top of the tanks. Do not release the pressure by opening the vent cocks on the bellows. Adjust the equipment for dive error as described in Section 13E5.

15A11. Calibration of Bendix log in shop. Shop calibration of the Bendix underwater log is accomplished in the following manner:

a. Set the B-adjustment to zero and the A1-adjustment to the factory adjustment setting as indicated on the plate which is mounted on the lower right-hand corner of the main mounting plate.

b. Energize the instrument.

c. With the water levels at the zero knot line of the knot scale and valves and vent cocks at the operating (speed) position, set the pointer at zero by means of the C-adjustment as described in Section 13A4.

d. Raise the water level in the dynamic pressure tank to 5 knots and make the pointer indicate 5 knots, plus or minus 0.10 knot, by turning the A2 adjustment ring. The red marks on the ring should line up with the scribe marks on the axle.

e. Raise the water level to 10 knots and observe the speed pointer. If it reads more than 10.1 knots, turn the plug at the bottom of the A spring until the pointer indicates 9.9 knots.

 
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f. Lower the dynamic water level to 5 knots on the scale and repeat the operations outlined in Section 15A11d.

g. Raise the dynamic water level to 10 knots on the scale and repeat the operations outlined in Section 15A11e.

h. Repeat the operations outlined in Sections 15A11f and 15A11g until the speed

  indications of 5 knots plus or minus 0.10 knots, and 10 knots plus or minus 0.10 knots are obtained. If, when raising the dynamic water level to 10 knots on the scale, a speed indication of less than 9.9 knots is obtained on the speed dial, turn the plug below the A-spring outward until a speed indication of 10.1 knots is obtained.
 
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