Electro-Chemical Devices (ECD) SMS22 - Manual (Page 17)

3.0 OPERATION
This section will provide a basic overview of the RUN, PRIME and CALIBRATE functions of the SMS-22
Analyzer. The Menu structure and the functions of the MENU SELECT keys and the CALIBRATE keys.
3.0.1 RUN Function
The ECD SMS-22 is a sequential sampling analyzer. RUN sequences through the following analysis cycle;
1. Fill the measurement cell with sample and drain (Rinse Cycle)
2. Fill and drain (Rinse Cycle)
3. Add caustic and Fill (Sample)
4. Mix the solution and measure the Sulfide ion
5. Adjust the Sulfide 4-20mA output signal
6. Add acid, mix, measure the pH
7. Adjust the pH 4-20mA output signal,
8. Drain the flow cell and repeat the cycle.
MVS10 Sulfide Ion Electrode only measures the sulfide
ion (S
-2 ) component of the total sulfide present in the
sample. It does not “see” bisulfide (HS - ) or hydrogen
sulfide (H
2
S). The pH of the sample must be raised to
convert most of the H
2
S and bisulfide into sulfide ion.
The S -2 proportion of the total sulfide varies from 0%
at pH 9 to 100% at pH 15, see Figure 3.1. The PHS10
pH sensor provides the pH value needed to calculate
the total amount of sulfides present in the water.
After the caustic, 16% KOH, has been added and the
sulfide measurement made, the sample is neutralized
with 6.5% HCl to bring the pH back into the neutral
range. The reaction, HCl + KOH → KCl + H
2
O, hydrochloric acid plus potassium hydroxide forms
potassium chloride and water which can be sent to the drain or added back to the sample water.
3.0.2 PRIME Function
The PRIME function powers Reagent pumps #1 and #2 and the Sample pump until it is switched off. This
allows the pumps to be easily primed after refilling the reagent bottles or changing the peristaltic
tubing. The Drain is Open and the 4-20 outputs are locked while the PRIME switch is ON.
3.0.3 CALIBRATE Function
The CALIBRATE function cuts the power to all of the pumps and drain valve. The 4-20 outputs are locked
while the CALIBRATE switch is ON. This allows the sensors to be removed from the flow cell and
calibrated in standard solutions.
0
20
40
60
80
100
10 12 14
pH
% Sulfide vs pH
% S-2
SMS-22 Page 8