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Lead Contents

Level Switches

These devices equip electrodes to detect liquid levels. They have been widely used in water works and sewers for buildings and housing complexes, industrial facilities and equipment, water treatment plants and sewage treatment facilities, and many other applications.

Overview Features
Principles Classifications
Engineering Data Further Information

Related Contents

Primary Contents

Level Controller Selection Criteria

Categories (Reference Information)

Categorized by Fluid Types

Applicable liquidsElectrodeElectrode HoldersRelay Unit
Acid/alkaline solutionsSelect electrodes based on corrosion resistance Table 4.
(Separators are not used.)
Electrodes in BS-IT are outlined in Table 4.
Separate each electrode with insulation.
Low-sensitivity 61F-[][]ND Level Controller (61F-11ND or equivalent, however depending on the cable length, the long-distance 61F-11NL
Level Controller may be required.)
BoilerSUS316 (The materials used make the water alkaline.)BS-1 (Subject to high temperature and pressure.)Standard 61F-[][] Level Controller
Tap waterSUS304, SUS316PS, BF. No other specific requirements.Standard 61F-[][] Level Controller, but when it is over a long distance, use a long-distance 61F-[][]L Level Controller.
Pure water
(Ion-exchanged water)
Titanium (Maintains the purity level of water.)BS-1T TitaniumMay require a high-sensitivity Level Controller depending on conductivity 61F- [][]NH (61F-11NH) Ultra-high-sensitivity 61F-UHS Level Controller
Bubbles (Detection)SUS304, SUS316, Titanium
(Separators are not used.)
PS, BFHigh-sensitivity 61F-GP-NH Level Controller or equivalent
Bubbles (No detection)As above (Separators are not used.)As aboveLow-sensitivity 61F-[][]ND Level Controller
WastewaterSUS304 (Low sainity)
(Separators are not used.)
BF-1 is used with each electrodes separated.Low-sensitivity 61F-[][]ND Level Controller
Oil mixed in waterSUS304PS, BF use pipes to guard against the oil.Standard 61F-[][] Level Controller
SteamSUS316PS-1, BF-1
If there is enough pressure to be able to separate the electrodes, use the BS-1.
Standard 61F-[][] Level Controller

Categorized by Installation Conditions of Electrodes

Installation ConditionElectrodeElectrode Holder
Confined spacePH underwater electrodes---
Protect against rainwaterSUS304, SUS316PS + F03-11 Protective Cover + F03-12 Frame
Objects from wastewater (i.e.,clothing)
get tangled
SUS304The BF-1; separates the distance between electrode
holders
Wastewater, contaminated water, or
areas with clusters of grease
SUS304 or SUS316As above
Elevated tankSUS304 or SUS316PS
Ground tankSUS304 or SUS316, F03-05 Electrode
Band, PH underwater electrodes
PS
Sewer, drains (manhole)SUS304, SUS316PS (Place the electrodes in a pipe in areas that
accumulate grease, e.g., underground, factory pits)
Septic tank (Flushed matter)SUS304BF-1
Measurements at a depth like water
wells
PH underwater electrodes---
Areas where ice formsPH underwater electrodes---
High temperature (hot water tank)SUS316Temperatures under 50°C, BS-1S2
No model is suitable for temperatures above 250°C
(Must be made by the user.)

Selection Criteria for 61F Level Controllers

Specific Resistance and Model Selection Criteria

The limit for specific resistance of liquid that can be controlled with a generic Level Controller is 30 kΩcm when using a PS-3S Electrode Holder within a submersion depth of 30 mm. For any fluid with specific resistance higher than this value, use a high-sensitivity Level Controller (H type). (See note.)

Table 1 and Table 2 shown upper and Table 3 below show specific resistances for typical liquids. Use these when selecting a model.

Note:

1. The high-sensitivity Level Controllers may suffer from resetting problems when used with certain types of water. In some cases it cannot substitute for the standard Level Controllers or Low-sensitivity Level Controllers. Be sure to select the model appropriate for the application.

2. The circuit configuration of the High-sensitivity 61F-[ ]H Level Controller is designed so that the relay is reset when there is water present between the electrodes. When power supply voltage is applied, the internal relay switches to the NO contact and, when there is conductivity between electrodes E1 and E3, the relay is reset to the NC contact.
This contact operation is reversed for models other than the high-sensitivity models. Although the internal relay operates (and operation indicator turns ON) simply when the power supply voltage is applied, this operation is normal. (The relay in the 61F-[ ]NH energizes when there is water present between the electrodes.)

Note:For the ultra high-sensitivity variable 61F-HSL Level Switch, malfunction due to electric corrosion may occur in the DC electrode circuit. Be careful not to use the product where current constantly flows between electrodes.

Table 1: Specific Resistance of Water (General Guideline)

Type of waterSpecific Conductance
Tap water5 to 10 kΩ · cm
Well water2 to 5 kΩ · cm
River water5 to 15 kΩ · cm
Rainwater15 to 25 kΩ · cm
Seawater0.03 kΩ · cm
Sewage0.5 to 2 kΩ · cm
Distilled water250 to 300 kΩ · cm min.

Table 2: Detectable Specific Resistance (Guideline)

Type of waterSpecific resistance (recommended value)
Long distance (4 km)5 kΩ · cm max.
Long distance (2 km)10 kΩ · cm max.
Low sensitivity10 kΩ · cm max.
Two-wire10 kΩ · cm max.
General-purpose10 to 30 kΩ · cm
High-temperature10 to 30 kΩ · cm
High-sensitivity (COMPACT plug-in type)30 to 200 kΩ · cm
High-sensitivity (base type)30 to 300 kΩ · cm
Ultra high-sensitivity100 kΩ to 10 MΩ · cm

Note: The specific resistance of liquids are those that can be controlled using the PS-3S when the submersion depth is 30 mm or less.

Conductance

Conductance is a scale describing how easily current can flow. The relationship of Conductance and resistance is defined by the following equation.

Table 1 can be modified to contain the corresponding conductance as shown in Table 1A.

Table 1A: Specific Conductance of Water (Guideline)

Type of waterSpecific Conductance
Tap water100 to 200 μS/cm
Well water200 to 500 μS/cm
River water67 to 200 μS/cm
Rainwater40 to 67 μS/cm
Seawater33,300 μS/cm
Sewage500 to 2,000 μS/cm
Distilled water3.3 to 4 μS/cm max.

Table 3: Specific Resistance of Various Liquids

Type of liquidTempera-ture
(°C)
Concen-tration
(%)
Specific resistance
(Ω・cm)
Beer (Company A)
Port wine (Company K)
Whisky (Company T)
Sake (Company K First grade quality)
12
12
12
12
---
---
---
---
830.0
966.0
14,608.0
1,743.0
Silver nitrate AgNO3185.0
60.0
39.5
4.8
Barium hydroxide Ba (OH)2181.25
2.5
40.0
20.9
Calcium chloride CaCl2185.0
20.0
35.0
15.6
5.8
7.3
Cadmium chloride CdCl2181.0
20.0
50.0
181.0
33.5
73.0
Cadmium sulfate CdSO4181.0
5.0
35.0
240.0
68.5
23.8
Nitric acid HNO318
15
15
5.0
31.0
62.0
3.9
1.3
2.0
Phosphoric acid H3PO41510.0
60.0
87.0
17.7
5.5
14.1
Sulphuric acid H2SO4185.0
30.0
97.0
99.4
4.8
1.4
12.5
117.6
Potassium bromide KBr155.0
36.0
14.5
2.9
Potassium chloride KCI185.0
21.0
14.5
3.6
Potassium chlorate KClO315527.2
Potassium cyanide KCN153.25
6.5
19.0
9.8
Potassium carbonate K2CO3155.0
30.0
50.0
17.8
4.5
6.8
Potassium fluoride KF185.0
40.0
15.3
4.0
Potassium iodide KI185.0
55.0
31.4
2.4
Potassium nitrate KNO3185.0
22.0
22.1
6.2
Potassium hydroxide KOH154.2
33.6
42.0
6.8
1.9
2.4
Potassium monosulfide K2S183.18
29.97
47.26
11.8
2.2
3.9
Copper sulfate CuSO4182.5
17.5
92.6
21.8
Ferrous sulfate FeSO4180.5
3.0
65.0
21.7
Hydrogen bromide HBr155.0
15.0
5.2
2.0
Hydrochloric acid HCl155.0
20.0
40.0
2.5
1.3
1.9
Hydrogen fluoride HF180.004
0.015
0.242
29.8
4,000.0
2,000.0
275.0
2.9
Mercuric chloride HgCl2180.229
5.08
22,727.0
2,375.0
Hydrogen iodide HI1557.5
Potassium sulfate K2SO4185.0
10.0
21.8
11.6
Sodium chloride NaCl185.0
25.0
14.9
5.6
Sodium carbonate Na2CO3185.0
15.0
22.2
12.0
Sodium iodide NaI185.0
40.0
33.6
4.7
Sodium nitrate NaNO3185.0
30.0
22.9
6.2
Sodium hydroxide NaOH152.5
20.0
42.0
9.2
2.9
8.4
Sodium sulfate Na2SO4185.0
15.0
24.4
11.3
Ammonia NH3150.1
4.01
3.05
3,984.0
913.0
5,181.0
Ammonium chloride NH4Cl185.0
25.0
50.5
2.5
Ammonium nitrate NH4NO3155.0
50.0
16.9
2.7
Ammonium sulfate (NH4)2SO4155.0
31.0
18.1
4.3
Zinc chloride ZnCl2152.5
30.0
60.0
36.2
10.8
27.1
Zinc sulfate ZNSO4185.0
30.0
52.4
22.5

Selecting Electrode Material According to Resistance against Corrosion

To get the most out of the electrodes, refer to Table 4 to select the best material.

Table 4: Resistance to Corrosion of Electrode Material

AqueousSolutionElectrodematerial
TypeConcentration (%)Temperature (°C)SUS
304
SUS
316
TitaniumHAS
B
HAS
C
SulphurousacidH2SO3630ECABB
Sulphuric acid H2SO4130AAAAA
1BPEDEBC
330BAAAA
3BPEEECC
530DBDBA
5BPEEEDD
1030ECEAA
10BPEEDCE
2030EECCB
20BPEEDDE
4030EEDBB
40BPEEDEE
6030EEDBC
60BPEEDCD
7030EEDBB
70BPEEDCD
8030EEDBB
80BPEEDDD
9030EEDBB
90BPEEDDD
9530EDDBB
95BPEEDDD
Hydrochloric acid HCl130EDBBA
1BPEEEDC
330EEBBA
3BPEEEDC
530EECCA
5BPEEEED
1030EEECC
10BPEEEEE
1530EEECC
15BPEEEEE
2030EEECD
20BPEEEEE
3730EEECE
37BPEEEEE
Chromium oxide CrO310BPDCABC
2030CBABB
36.590EECCC
Nitric acid HNO31030BAADA
10BPBBBDC
20290BBCDD
65175CCBEE
6830CCADD
68BPDDBEE
9080EEAEE
HydrogenfluorideHF530EEDDC
10030EDCCC
PhosphoricacidH3PO410 to 85RTBBCBC
AceticacidCH3COOH5 to 50RTAAAAA
100RTAAAAA
100BPCBAAA
FormicacidH·COOHAllBPDDDAA
Acetone CH3·CO·CH3AllRTBBAAA
AlumAllRTEEDBB
Aluminum sulfate50BPDCBCA
Ammonium chloride NH4Cl5BPDDABB
Ammonium nitrate NH4NO3AllBPAAABB
Ammonium sulfate (NH4)2SO45RTEDBBC
10BPEEBBC
Ammonia NH3100100CCABB
10BPCBBBC
2860CBABB
Potassiumhydroxide KOH25BPBACBC
SodiumhydroxideNaOH3060AABAB
5065BACAC
Sodium carbonate Na2CO325BPBBBBB
Potassium carbonate K2CO320BPBBBBB
Zinc chloride ZnCl250150DCBBC
Calcium chlorideCaCl225BPCCAAA
Sodium chlorideNaCl25BPCBABB
Ferric chloride30RTEEAEB
Copper chloride30RTEEAEB
Sea waterRTCCABA
HydrogenperoxideH2O210RTBBBBB
Sodium sulfite10RTBBABB
Citric acidAllRTBACAA
OxalicacidCO2H·CO2HAllRTBADBB
Sodium hypochlorite10RTEDACC
Potassium dichromate10BPCBABC
Magnesium chloride30RTCBAAA
Magnesium sulfate10RTBBAAA

Note:

1. RT: Room temperature
BP: Boiling point

2. A: Adequate resistance to corrosion
B: Resistive to corrosion, erosion rate is less than 0.8 mm/year
C: Low resistance to corrosion, erosion rate is less than 1.8 mm/year
D: Highly corrosive, not usable
E: No resistance to corrosion, not usable

3. The table above is used for reference when selecting the electrodes. Even if the material has adequate corrosion resistance, it doesn't mean that it is not subject to corrosion.
Check regularly once a month to see if corrosion is occurring. If it is, replace the electrodes.

Reference

When selecting an Electrode Holder, make sure that you consider the corrosion resistance of the material of electrode holders as it may be exposed to the liquid inside the water tank.