Myron L 729II - Manual (Page 53)

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V. COMPONENT IDENTIFICATION,
CALIBRATION AND PREVENTIVE CARE
B. METER MECHANICAL ZERO PROCEDURES
ANALOG METERS ONLY
1. Ensure power is OFF.
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 to Section V.C.
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. See figure II.G.9.
4. Insert a small standard screwdriver into the access hole
and carefully locate the slot in the mechanical
adjustment plug.
5. Turn the adjustment plug slightly until the needle rests
on zero.
6. Insert the small plastic button into the access hole.
7. Turn power ON.
C. CALIBRATION PROCEDURES
All Myron L pH/ORP Monitor/controllers are factory calibrated
prior to shipment and are ready to install without further
calibration. Calibration should be checked occasionally with the
internal ZERO Test switch (ZERO) to ensure continued accuracy.
The following procedures are provided in the event that
recalibration becomes necessary.
For electronic calibration the only equipment required is a tweaker
or small screwdriver.
For wet calibrating a pH Monitor/controller the only items required
is a tweaker or small screwdriver, and pH buffer solutions; 4, 7
and/or 10.
pH 7 Buffer solution is recommended to wet calibrate ORP ZERO.
The electronic calibration is recommended for SPAN calibration
and adjustment, as described in “SPAN (GAIN/SLOPE)
Calibration” section V.C.1.b.
Refer to Figure V.A.1. to locate the components described in this
section.
NOTE: When opening instrument, remove front cover with care;
a ribbon cable connects the front panel and main board.
When performing calibration procedures, the
technician must take extreme care to avoid
contacting the circuitry other than the Calibration
controls. Failure to do so could result in damage to
the equipment, property and/or personal injury.
1. ELECTRONIC CALIBRATION (CIRCUIT ONLY)
This method is faster than the following method using buffer
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 negligible.
The DISplay calibration controls have been SET and SEALED
prior to leaving the factory, and under normal conditions will not
require readjustment. This allows the customer to use the panel
meter/display to easily set the electronic calibration as described
below.
NOTE: If the DISplay calibration controls have been adjusted it
will be necessary to calibrate the RECORDER Output as
described in “0-10VDC RECORDER OUTPUT Calibration” section
V.C.2.
a. ZERO Calibration - 7pH or 0mV
1. Turn power OFF.
2. Using a standard slot screwdriver remove the
screws on the front panel.
3. Carefully wiggle the front panel to loosen the gasket and
pull gently toward you. Do not pull more than about 8
inches/20CM or you could damage the wiring harness.
4. Turn the front panel around so that the back side is
facing you and set aside.
5. Turn power ON.
6. Press and hold the ZERO Test Switch. The display
should indicate 7.00pH or 0mV (ORP). If not, set to
7.00pH or 0mV with the ZERO calibration control.
7. Turn power OFF
8. Continue with SPAN Calibration, or re-install front panel
as described in “REASSEMBLY”, page 54.
b. SPAN (GAIN/SLOPE) Calibration
1. Press and hold the SPAN Test Switch. The display
should indicate 0pH or -1999mV (ORP). If not, set to 0pH
or -1999mV with the SPAN calibration control.
2. End of calibration, turn power OFF
3. Re-install front panel as described below in
“REASSEMBLY”.
2. 0-10VDC RECORDER OUTPUT Calibration
For recorder output voltages other than 0-10VDC, substitute as
required, i.e. 5.00VDC = 2.50VDC per Section II.F.2.
pH Models
On pH models, the ZERO (7.00pH) test switch and the ZERO
calibration control are used to adjust the recorder output, 7.00pH
equals 5.00VDC. The display is then adjusted to indicate 7.00pH
with the DISplay calibration control. The SPAN test switch and
the SPAN calibration control are used to adjust the span of the
recorder output to 0VDC (0pH). Refer to figure V.A.1 for location
of items described below. A DVM set to DC Volts is required.
1. Ensure power is OFF.
2. Attach DVM to RECORDER output connection.
3. Turn power ON.
4. Press and hold the ZERO test switch.
5. The DVM should indicate 5.00VDC.
6. If not, adjust ZERO calibration control until DVM
indicates 5.00VDC.
7. Verify the panel meter/display, it should indicate 7.00pH.
8. If not, adjust DISplay control until display indicates
7.00pH.
9. Press and hold the SPAN test switch.
10. The DVM should indicate 0VDC.
11. If not, adjust SPAN calibration control until DVM
indicates 0VDC.
12. Display does not require further adjustment.
13. Turn power OFF.
14. Re-install front panel as described in
“REASSEMBLY”, page 54.
ORP Models
On ORP models, the ZERO (0mV) test switch and the ZERO
calibration control are used to adjust the recorder output, 0mV
equals 5.00VDC. The display is adjusted to indicate 0mV with the
ORP ZERO calibration control. The SPAN test switch and the
SPAN calibration control are used to adjust the span of the
recorder output to 0VDC (-1999mV). The display is then adjusted
to indicate -1999mV with the DISplay calibration control. Refer to
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CAUTION - READ FOLLOWING CAREFULLY