Myron L 767 - Manual (Page 14)

Component Identification/Calibration and Preventive Maintenance
4.2 METER MECHANICAL ZERO PROCEDURES
Models 756, 757 & 767 (Analog Meters Only)
STEP 1 Turn OFF or disconnect the Monitor’s main AC power.
STEP 2 Note the position of the meter needle. If it has come to rest
pointing at the zero mark on the scale, turn the Monitor back
ON and continue on the Section 4.3.
STEP 3 Locate the small (approx. 1 / 4 ”), black plastic button directly
below the center of the meter. Use a small screwdriver or a
fingernail to gently pry it loose and remove it from the access
hole.
STEP 4 Insert a small standard screwdriver into the access hole and
carefully locate the slot in the mechanical adjustment plug.
STEP 5 Turn the adjustment plug slightly until the needle rests on
zero.
STEP 6 Insert the small plastic button into the access hole.
STEP 7 Turn ON or reconnect the Monitor’s main AC power.
4.3 CALIBRATION PROCEDURES
All Myron L Conductivity Monitors/Controllers are factory calibrated
prior to shipping and are ready to install without further calibration.
Calibration should be checked occasionally with the internal
Calibration Test switch (SW1) to ensure continued accuracy. The
following procedures are provided in the event that re-calibration
becomes necessary. The only equipment required are a small
screwdriver, standard solution, and an accurate multimeter. Calibration
should be accomplished by a qualified technician.
Refer to Fig. 4-1 to locate the components described in this section.
CAUTION!
When performing calibration procedures, the technician must take
extreme care to avoid contacting the fuse or control circuitry other than
trimmer calibration screws. Failure to do so could result in damage to
the equipment and/or property.
4.3.1 CALIBRATION PROCEDURES USING STANDARD SOLUTION
The best method of recalibrating your conductivity monitor/controller is
with NIST traceable Standard Solution (available from your Myron L
Company distributor, or elsewhere). Because it includes the sensor,
the entire instrument is recalibrated.
Step 1 Obtain a standard solution which is 60-90% of full scale of
the instrument.
Step 2 Adjust the temperature of the standard solution to 25
°
C. This
may be accomplished by using a warm or cool bath for the
bottle.
Step 3 Obtain a clean glass beaker. Rinse beaker thoroughly with
the standard solution. Place cell (sensor) of instrument in the
beaker of standard solution. Level of standard solution
should be high enough to cover
1 / 2 " above bore hole. Slowly
shake the sensor to remove air bubbles from inside the
sensor bore hole.
Step 4 Allow 3-4 minutes for temperature to equilibrate. Read the
display of the instrument. The display should match the
value and units of measure located on the bottle of standard
solution. If the reading is different, adjust R25 on the main
circuit board until the reading matches the solution value.
This will require removal of the front cover. NOTE: Remove
front cover with care; a ribbon cable connects the front
panel and main board.
4.3.2 CALIBRATION PROCEDURES (CIRCUIT ONLY)
This method is faster than the method using standard solution, but it
does not include the sensor. Therefore, it should be used only in
applications where the chance of sensor contamination or damage are
slight.
4.3.2.1 MODEL 755
STEP 1 Connect a voltmeter (0-10 VDC) to the Recorder output
terminals TB2-6 & 7 with the positive (+) lead on TB2-7.
STEP 2 Press and hold the Calibration Test switch (SW1). The
voltmeter should indicate +10 volts. If not, set to +10 volts
with the Main Calibration trimmer (R9).
STEP 3 Set the front panel control knob to the full scale setting. With
the Calibration Test switch (SW1) still depressed, rotate the
front panel control knob above and below the full scale
setting several times to locate the setting at which the front
panel LEDs switch. You should find one upper setting where
the LEDs switch from red to green and one lower setting
where they switch from green to red. The full scale index
mark should be halfway between these two settings. If
necessary, loosen the control knob set screws and reposition
the knob. This completes the calibration.
4.3.2.2 MODELS 756, 757 & 758
STEP 1 Connect a voltmeter (0-10 VDC) to the Recorder output
terminals TB2-6 & 7 with the positive (+) lead on TB2-7.
STEP 2 Press and hold the Calibration Test switch (SW1). The
voltmeter should indicate +10 volts. If not, set to +10 volts
with the Main Calibration trimmer (R9).
STEP 3 With the Calibration Test switch (SW1 ) still depressed, set
the Front Panel Meter trimmer (R25) for a full scale
indication on the panel meter. If you have a digital readout
(model 758), set it to 1999 (decimal point omitted) for ranges
0-20, 200 or 2000. For all other ranges, set it to read the
range maximum. If not known, this can be determined by
looking up the range suffix on the enclosure’s model label in
the list on page 3 of this manual.
Example: For model 758-11 (0-50 µ S), set front panel LCD to indicated
50.0
µ
S.
4.3.3 MODEL 758 WITH 4-20 mA OR 4-20D OPTION
NOTE: FOR 4-20D, PROCEED TO STEP 1.
CAUTION! FOR 4-20mA OPTION ONLY
The proper supply voltage (V Supply) and load resistance (R) must be
selected. Failure to do so could result in damage to the 758 optional
panel board.
NOTE:
The proper load resistance (in ohms) is found by using the formula
and/or chart as shown in Fig. 4-2.
STEP 1 Set the controls of a test meter to read at least 20mA and
connect it between the positive terminals of the Transmitter
and Receiver as shown in Fig. 4-3 (4-20 mA option) and Fig.
4-4 (4-20D option).
STEP 2 Press and hold the “SET POINT CHECK” switch. It must be
depressed during all the following adjustment steps.
STEP 3 Turn the Set Point trimmer (R28) until the meter displays a
reading 0.00.
STEP 4 Turn the 4-20 mA Null trimmer (R23) (see Fig. 4-1 ) until the
test meter indicates 4 mA.
STEP 5 Readjust the Set Point trimmer (R28) until the meter displays
1999 (decimal point omitted).
STEP 6 Turn the 4-20 mA Full Scale trimmer (R20) (See Fig. 4-1 )
until the test meter indicates 20 mA.
STEP 7 Repeat STEP 3 through STEP 6, readjusting as required.
STEP 8 Reset the set point to the desired setting. Release the “SET
POINT CHECK” switch.
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