digital conductivity meter service manual

DIGITAL CONDUCTIVITY METER SERVICE MANUAL

MODEL 1152 SERVICE MANUAL

EMCEE ELECTRONICS, INC.

520 CYPRESS AVENUE

VENICE, FL 34285

(941) 485-1515

FAX 941-488-4648

The information contained in the accompanying document is proprietary and confidential, and may not be copied in any manner whatsoever without prior written consent of Emcee Electronics,

Inc. The document and the material therein may not be used for any purpose other than that intended by Emcee Electronics, Inc.

COPYRIGHT 2002 EMCEE ELECTRONICS, INC.

REVISION DATE: FEBRUARY 23, 1996

PAGE 1 OF 14


TABLE OF CONTENTS

PAGE

1.0 GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . 3

2.0 TEST EQUIPMENT REQUIREMENTS . . . . . . . . . . . . . 3

3.0 PRELIMINARY CALIBRATION CHECK . . . . . . . . . . . . 3

4.0 BATTERY REPLACEMENT . . . . . . . . . . . . . . . . . 4

5.0 CIRCUIT DESCRIPTION . . . . . . . . . . . . . . . . . 4

6.0 TROUBLE SHOOTING CHART . . . . . . . . . . . . . . . 6

7.0 CALIBRATION . . . . . . . . . . . . . . . . . . . . . 6

8.0 TEST PROCEDURE . . . . . . . . . . . . . . . . . . . 7

9.0 PARTS LIST . . . . . . . . . . . . . . . . . . . . . 8

10.0 ILLUSTRATIONS

FIGURE 1 METER AND PROBE . . . . . . . . . . . . . 9

FIGURE 2 PROBE ATTACHMENT . . . . . . . . . . . . . 9

FIGURE 3 PROBE CALIBRATION NO. . . . . . . . . . . 9

FIGURE 4 OPERATING POSITION . . . . . . . . . . . .10

FIGURE 5 CALIBRATION MODE . . . . . . . . . . . . .10

FIGURE 6 MEASURE MODE . . . . . . . . . . . . . . .10

FIGURE 7 ACCESSORY CABLE REEL . . . . . . . . . . .11

FIGURE 8 REEL - METER ATTACHMENT . . . . . . . . .11

FIGURE 9 METER INTERNAL VIEW . . . . . . . . . . .12

FIGURE 10 PC BOARD ASSEMBLY . . . . . . . . . . . .13

FIGURE 11 CALIBRATION ACCESSORY . . . . . . . . . .13

FIGURE 12 SCHEMATIC DIAGRAM . . . . . . . . . . . .13

SERVICE AND WARRANTY POLICY

See Service & Warranty Manual





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1.0 GENERAL DESCRIPTION

1.1 The Emcee Digital Conductivity Meter model 1152 as shown in Figure 1 is a hand held, battery operated, instrument for determining the conductivity of fuel samples. Technically, the instrument is a high range ohmmeter capable of reading between 500 megohms (2000 CU) and infinity (0 CU).

1.2 The controls as shown in Figure 1 consist of a pushbutton switch marked

M (measure) and a pushbutton switch marked C (calibrate).

1.3 Figure 2 shows the instrument with the probe attached and ready for fuel test.

1.4 Figure 6 shows the instrument in operation with the probe in a fuel sample.

1.5 The Accessory Cable Kit is shown in Figure 7 and 8. With this reel the instrument can be used to test fuel in a large storage tank.

1.6 Figure 10 shows the instrument with the back removed, and the plug in pre-amp and analog to digital PC boards removed.

1.7 Figure 11 shows the CU Substitution Box for complete calibration.

2.0 TEST EQUIPMENT REQUIREMENTS

2.1 CU Substitution Box

2.2

Digital Voltmeter, 10 megohm impedance 0-1 volt +/- .001 0-20 volt

+/- .01.

3.0 PRELIMINARY CALIBRATION CHECK

3.1 Attach probe to bottom connector on the conductivity meter.

3.2 Depress measure switch (marked M). The display should indicate 000 +/-

001 after 3 seconds. If the display does not indicate 000 +/- 001 remove the probe and recheck for zero. If the meter will zero without the probe but not with the probe, the probe should be rinsed with isopropyl alcohol and allowed to air dry before retesting. If the meter will not zero without probe, proceed to calibration procedure.

3.3 Depress calibration switch (marked C). The display should indicate the number on the probe (Figure 3) times 10 +/- 005.

Example: Probe No. = 42

Display = 415 – 425





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4.0 BATTERY REPLACEMENT

4.1 The model 1152 Conductivity Meter has an internal battery checking circuit. If batteries are weak the meter will read for a short time and shut itself off. If batteries are very low the unit will not turn on.

4.2 When battery replacement is indicated remove the 4 screws holding the back plate exposing the battery housing at the top of the meter.

4.3 Remove the 2 screws on the battery housing and set housing cover to one side (Figure 10).

4.4 Observe the polarity markings and insert three new batteries as shown in

Figure 10. Battery replacement must be (3) 6 volt Alkaline Nema 1414A Emcee

P/N 152-90-5341. Any other battery replacement will invalidate the CSA and

UL Intrinsically Safe Rating.

4.5 Replace back panel, check zero and calibration.

5.0 CIRCUIT DESCRIPTION

5.1 Power Supply The model 1152 Digital Conductivity Meter uses (3) A-554 6 volt batteries as a single 18 volt power source. Depressing either the measure or calibrate switches provides power to op amp 1 via D(1) or D(2).

Op amp 1A compares the battery voltage to a positive output at 6 volt zener reference (ZD-1) and provides a positive output at pin 1 if the battery voltage is above 13 volts. This insures adequate voltage for good regulation via VR-1. VR-1 provides a +10 volt (pin 1) and a +5 volt (pin 2) output in reference to pin 4. The +5 volt (pin 2) output in reference to pin 4. The

+5 volt output is buffered with op amp 1B. The 0 level reference voltage is developed using the output on op amp 1B pin 7. From this reference point we now have a +5 volt source and a -5 volt source.

The 0 reference voltage is not attached to the case. Resistors R-15 and R-16 make up a voltage divider to provide a -1 volt source which is tied to the case. The -1 volt becomes the bias voltage for the fuel probe.

5.2 CALIBRATE REFERENCE - The calibrate voltage is supplied by Q-1 and is adjustable from 0 to -1 volt. Q-1 is biased on in a saturation mode via R-14 when the calibrate switch is depressed. The collector output is divided by

R-21 and R-20 and the adjustable voltage is passed on to the pre-amp. When the measure switch is depressed R-13 reverse biases Q-1 and turns Q-1 off.

This action guarantees a 0 volt potential to the pre-amp calibrate input.





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5.3 Pre-Amp PC Board - P/N 152-04-0000 The pre-amp board is a separate plugin PC board. Due to the extreme high impedance of the circuit, this board is very sensitive to humidity. After manufacture, this board is coated with a conformal coating to reduce outside humidity effects. Since this coating cannot be removed, the components on this board should not be replaced. Any failure of the pre-amp board requires a new board assembly. The operation of this board, however, is to develop a current from the -1 volt bias through the fuel sample to the op amp pin 2. Pin 2 is maintained at 0 volts via the positive feedback through R3. With no fuel between the probe electrodes the pre-amp output should be zero. This is adjusted with zero adjust potentiometer R-19. During the calibrate period the negative voltage from R-

20 provides the bias source to the pre-amp and a calibrate reference can be set.

5.4 A-D Converter PC Board - P/N 152-05-0000 The A-D converter assembly is a plug-in PC board. The converter is basically a 0 - 1.999 volt., 3 digit voltmeter. The reference voltage for setting the A-D gain is adjusted by setting R-18 for approximately 1.0 volts. The final adjustment for this potentiometer, however, is dependent on R-3 tolerance and variations in the probe constant. The pre-amp output is fed to the A-D converter which has an automatic zero adjustment, therefore, any output from the amp can be directly monitored. The A-D converter directly drives the liquid crystal display located on the display PC board. The A-D board can be factory repaired.

5.5 Display PC Board P/N 152-03-0000 The display board includes the power regulator, reference voltage supply, calibration adjustment controls, liquid crystal display, measure and calibrate switches, and the interconnects for the A-D and the pre-amp boards. The display board can be factory repaired.





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6.0 TROUBLE SHOOTING CHART

MALFUNCTION PROBABLE CAUSE CORRECTIVE ACTION

Meter does not zero Contaminated Probe Clean thoroughly

with isopropyl

alcohol and air dry

Needs zero adjustment Adjust zero as per 7.2.

Meter reads above or Needs CAL adjustment Check Pre-amp output below calibration as per 7.0

number during CAL check

CU reading erroneous Contaminated or Clean probe with when CAL check is okay damaged probe. isopropyl alcohol

and air dry

Inspect probe for

physical damage.

Check electrical

characteristics as

per 7.0

No Display Indication Lack of supply Check connection and/or

voltage replace batteries

MEASURE/CAL switch Replace Display PC Bd.

defective P/N 152-03-0000

A-D Converter Replace A-D PC Bd.

defective P/N 152-05-0000

+/- 5 Supply In-op Replace Display PC Bd.

P/N 152-03-0000

7.0 CALIBRATION

7.1 With the back panel removed set R-18 (case hole marked CAL) to approximately mid scale. The exact setting is not important at this time, however, the voltage at A-15 should be approximately 1.0 volts above the zero reference (A-14).

7.2 Remove the probe if attached and depress the measure switch (M). Adjust

R-19 (case hole marked ZERO) for a display of 000 +/- 1.





PAGE 6 OF 14


7.3 Attach the CU substitution box directly to the conductivity meter using the 500 CU position.

7.4 Depress the measure switch (M) and adjust R-18 (CAL) for a display reading of 500 +/- 1.

7.5 Remove the substitution box and repeat the zero adjustment (7.2) if necessary. If zero adjustment is necessary repeat 7.3 and 7.4 after readjusting zero.

7.6 Attach the CU substitution box to the conductivity meter using the 100

CU position.

7.7 Depress the measure switch (M) and read the display for linearity. The display should read 100 +/- 1. If the display is outside of tolerance recheck zero and 500 CU positions.

7.8 Remove the plug from the unmarked hole in the case (between the ZERO and

CAL holes) to access R-20 (CAL reference).

7.9 Depress the calibrate switch (C) and adjust R-20 (Cal reference voltage) for a display or 400 +/- 1.

7.10 Replace the plug removed in step 7.8 (no additional adjustment of R-20 is necessary).

7.11 The instrument is now electrically standardized and should read ZERO =

000 +/- 001, CAL = 400 +/- 001, 500 CU BOX = 500 +/- 001 and 100 CU BOX = 100

+/- 001.

7.12 The meter is then adjusted to the probe for proper fuel measurements.

Identify the probe constant by locating the number stamped on the probe (Fig.

3). Multiply that number by 10 and adjust R-18 (CAL) for that number.

Example: Probe No. = 42 x 10 = 420

CAL adjust to 420 +/- 001

7.13 The meter is now properly calibrated for fuel measurements. Refer to section 8.0 for operating procedure.

8.0 TEST PROCEDURE

8.1 Attach probe to bottom connector on the conductivity meter.

8.2 Depress measure switch (M) with probe OUT of fuel sample. Reading should be 000 +/- 001 in approximately 3 seconds (Figure 4). If reading is outside limits remove probe and recheck zero by depressing measure switch.

8.2.2 If zero reading is outside of limits with probe removed, perform calibration procedure outline in section 7.0.





PAGE 7 OF 14


8.3 Depress Calibrate switch (C) with probe OUT of fuel sample. After 3 seconds reading should be 10 times the probe calibration number +/- 005

(Figure 5).

Example: Probe No. = 40

Meter Reading = 400 +/- 5 or 395 to 405

8.4 Insert probe in fuel to upper holes and depress measure switch. Report reading after 3 seconds for stabilization. Due to the polarization of the fuel sample the apparent reading will continue to change. Only the reading 3 seconds after depressing the measure switch is correct.

9.0 PARTS LIST

Batteries (3 required) 152-90-5341

Display PC Board 152-03-0000

Pre-Amp PC Board 152-04-0000

A-D Converter PC Board 152-05-0000

Probe 152-09-0000





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Figure 1

Figure 2

Figure 3





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Figure 4

Figure 5

Figure 6





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Figure 7

Figure 8





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Figure 9





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Figure 10

Figure 11





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Figure 12





PAGE 14 OF 14

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Table of contents