Model 1181Orp System Calibration; Orp Test Setup - Emerson Rosemount 1181pH TRANSMITTER Instruction Manual

MODEL 1181pH/ORP
Both ZERO and SPAN Controls are 20 turn
potentiometers. Several turns may be
required for proper calibration.
5. Generate a –1.000 VDC signal from the voltage
source. Adjust span control (under serial label) for
a 20 mADC output.
6. Repeat Steps 4 and 5 until calibration is correct.
3.5.4 Electronic Calibration Using a DC Voltage
Source. An output up to ±1.000 VDC is required as an
input to the 1181 ORP. Refer to Table 3-5 for the appro-
priate voltage required to simulate desired mV values.
Voltage listed are the American Con-
vention, reverse polarity for European Con-
vention.
TABLE 3-5.
Millivolt vs. Voltage Input
Millivolt Voltage Input
+1000 +1.000 VDC
+800 +0.800 VDC
+600 +0.600 VDC
+400 +0.400 VDC
+200 +0.200 VDC
0 0.000 VDC
The following calibration procedure is for a ±1000 mV
range.
1. Install connections from DC voltage source
between TB2-1 and TB2-2 on the Model 1181
ORP. Be sure to remove sensor wires from TB2-1
and TB2-2 while applying this voltage source.
2. Connect an ammeter capable of indicating 4 to 20
mADC between TB1-2 and TB1-3 in the Model
1181 ORP. Disconnect the analog meter or LCD
during this test.
3. Generate a +1.000 VDC signal from the voltage
source. Adjust zero control (under serial label) for
a 4 mADC output.
4. Generate a –1.000 VDC signal from the voltage
source. Adjust SPAN control (under serial label)
for a 20 mADC output.
5. Repeat Steps 3 and 4 until no further calibration is
required.
6. Reinstall sensor wires and analog meter or LCD (if
necessary). Refer to Figure 2-2, or 3-4.
24
NOTE
NOTE
Millivolt Voltage Input
–200 –0.200 VDC
–400 –0.400 VDC
–600 –0.600 VDC
–800 –0.800 VDC
–1000 –1.000 VDC
3.6 MODEL 1181 ORP SYSTEM CALIBRATION.
Upon completion of electrical calibration of the Model
1181 ORP, it may be desired to check the total system
operation by using a solution with a known oxidation-
reduction potential.
3.6.1 Quinhydrone Solution A commonly used ORP
standard solution is the saturated quinhydrone solu-
tion. This can be made quite simply by adding a few
crystals of quinhydrone to either pH 4 or pH 7 buffer.
Quinhydrone is slightly soluble, so only a few crystals
will be required. The solution is yellow-colored. The
resulting potentials, measured with a clean platinum
electrode and saturated KCl/AgCI reference electrode,
should be within ±20 millivolts of the value shown in
Table 3-6. These potentials may be measured from the
electrode lead wires that connect to terminals TB 2-1
and TB 2-2 of the Model 1181 ORP Transmitter (see
Figure 2-2). Solution must be noted to insure accurate
interpretation of results. The ORP value of saturated
quinhydrone solution is not stable over long periods of
time. These standards should be made up fresh each
time they are used.
CAUTION
Quinhydrone is Highly Acidic
TABLE 3-6.
ORP of Saturated Quinhydrone Solution
(Millivolts)
TEMPERATURE °C
Millivolt Potential
Adjust the ZERO Control for compensation of the
measuring electrode output.
FIGURE 3-4

ORP Test Setup

TB2
VOLTAGE
1
SOURCE
±1.000VDC
1181
2
ORP
UNDER
3
TEST
4
SECTION 3.0
START UP, AND CALIBRATION
pH 4 pH 7
20 25 30 20 25 30
268 264 260 94 87 80
TB1
+ +
1
+
2
+
- -
DMV
3
-
24
VOLT
P.S.