22
MODEL 1181pH/ORP
SECTION 3.0
START UP, AND CALIBRATION
3.3.3
If it is not practical to take a grab sample, rea-
sonable accuracy can be obtained by the buffer solu-
tion method (refer to paragraph 3.3.1). Exceptions to
this are streams or processes with chemical composi-
tions very different from buffer solutions such as high
purity water, miscible solvents and other dilute solu-
tions. The grab sample methods should be used for
solutions of this type.
3.4 OPERATION WITH A FIXED T.C.
In the event it is
desired to operate the Model 1181 pH with a fixed T.C.,
refer to Table 3-4 for the proper resistance value.
TABLE 3-4.
Resistance Value for Fixed T.C.
To compute the resistance values for temperature
other than those listed, use the following equations:
RTC = 2663 + (13.5 x °C)
RDC = 100 + (.385 x °C)
NOTE
When using a fixed T.C. with the Rose-
mount Analytical Model 381 sensor, con-
sult the 381 Instruction Manual.
After the appropriate resistor has been selected, dis-
connect the T.C. black and white leads going to pre-
amp and connect the resistor in their place (see Figure
2-4).
3.5 MODEL 1181ORP START-UP.
This paragraph
describes the range selection, electronic calibration,
and system calibration of Model 1181 ORP Two-Wire
Transmitter. The Model 1181 ORP is factory calibrated
for an ORP range of ±1000 mV. If a different range is
desired, refer to paragraph 3.5.1. If the ±1000 mV
range is suitable, proceed to paragraph 3.5.2.
3.5.1 Range Selection.
A matrix showing the switch
position of S1 for the various ranges is in Figure 3-1.
This switch is located on the circuit side of the enclo-
sure. See Figure 3-3 for ORP range switch selection
procedure. The following is an example of the switch
position required for ±200 mV range.
1.
The mid-scale mV range is 0 mV. Switches 6 and
7 must be closed and switches 5 and 8 must be
opened.
2.
A span of 400 mV is required. Switch 2 must be
closed and switches 1, 3, and 4 must be opened.
3.
Any mid-scale mV range between –1200 and
+1200 may be selected.
4.Spans between 200 to 2400 mV are available.
3.5.2 Polarity Selection.
The Model 1181 ORP is
calibrated in the American convention of millivolt
measurement, with 0 millivolt (mV) being mid-scale
(12 mADC). All positive potentials are downscale
and all negative potentials are upscale. The meas-
urement may be reversed to accommodate the
European convention (see Figure 6-2).
1.Remove jumper from 2 and 3.
2.Install jumper 1 and 4.
3.The Model 1181 ORP has now been modified to
accommodate the European convention. Negative
potentials downscale and positive upscale.
NOTE
Negative potentials are reducing indica-
tions and positive potentials are oxidizing
indications.
3.5.3 Electronic Calibration Using the Preamplifier.
The Model 1181 ORP may be calibrated using the pre-
amplifier within the ORP sensor.
1.
Retain all connections from the ORP sensor to the
Model 1181 ORP.
2.
Using a Model 213 pH/ORP Simulator or equiv-
alent, remove the ORP electrode connector from
the preamplifier and install the connector from the
Model 213 to the preamplifier.
3.
Install an ammeter capable of indicating 4 to 20
mADC between TB1-2 and TB1-3 in the Model
1181 ORP. Disconnect the indicating meter during
this test. If a LCD is used refer to paragraph 3.13 for
calibration.
4.
Place the Range Switch on the Model 213 for a
+1000 mV output. Adjust ZERO control (under
serial label) for a 4 mADC output.
Temperature
Ohms (3K RTC) Ohms (Pt-100)
0°C
2663
100.00
10°C
2798
103.85
20°C
2833
107.70
25°C
3000
109.62
30°C
3067
111.55
40°C
3202
115.40
50°C
3337
119.25
60°C
3472
123.10
70°C
3607
126.95
80°C
3742
130.80
90°C
3877
134.65
100°C
4012
138.50