Introduction to Industrial Automation

10.5   The Food Industry: A Machine for Production 

of Tzatziki Salad

In the food industry, the machine for production of Greek tzatziki (a kind of green salad made 

from cucumber, yogurt, and garlic) consists of:

 

◾

Three silos containing the raw materials

 

◾

Three electronic weighing scales with rotating platforms

 

◾

A conical tank vessel for mixing materials

 

◾

A drum blender

 

◾

A dosing pump

 

◾

The conveyor belt for packaging of the produced salad, as shown in Figure 10.5a.

Technical characteristics of the equipment.

  1. The outlet doors of silos open for feeding the weighing scales via the activation of the pneu-

matic cylinders C

1

, C

2

, and C

3

, which are extended at the rest state. Each cylinder is retracted 

by the activation of the corresponding PLC output.

  2. Each raw material falls on the corresponding weighing scale with a slaw rate of 100 gr/s. 

The electronic weighing scales have an SPST (NO) output, which is energized at each Kg of 

weight according to the graph shown in Figure 10.5b.

  3. The existent raw material on each scale after weighing, falls in the conical tank vessel 

via the activation of pneumatic cylinders C

4

, C

5

, and C

6

, which at rest state are also 

extended.

  4. The drum blender and the dosing pump have direct starting motors. At the bottom of the 

tank vessel there is a level sensor for viscous material with an SPST output that is NO when 

there is no material in the tank vessel.

  5. The conveyor belt operates with a direct starting motor (M

1

) and brings the plastic contain-

ers to be filled at specific positions.

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386

 

◾

  Introduction to Industrial Automation

Operation specifications. The production procedure includes three phases: weighing the raw 

materials, the feeding and mixing phase, and the packaging phase, which are performed sequen-

tially according to the following specifications:

  1. The production process starts with a momentary signal START from the push of a button. 

Then, the outlet doors of the silos open for feeding weighing scales until the required quan-

tity of material is completed at each scale. After the completion of a material quantity, the 

corresponding outlet door closes.

  2. When the three required quantities have all been completed on the weighing scales, the 

cylinders C

4

, C

5

, and C

6

 are retracted by activation of the corresponding outputs and cause 

them to fall in the tank vessel. The three cylinders remain retracted for 5 s in order to be sure 

that the viscous yogurt has fallen.

  3. At the end of the time interval of 5 s, the rotation of the blender starts and keeps on for 

12 min.

  4. After the end of the mixing procedure, the dosing pump and the conveyor belt start to oper-

ate simultaneously. The pump and the conveyor are synchronized by construction during 

the overall operation.

Mince

cucumber

Silos with

feedstock

Digital

balances

Yogurt

Mince garlic

Mixture tank

Blender

Dosing pump

Level sensor

Balance

SPST output

Packaging belt conveyor

Closed

Open

Weight

Kg

1

2

3

4

C

1

C

2

C

3

C

6

C

5

C

4

Z

3

Z

2

Z

1

Z

1

Z

2

Z

3

M

1

F

1

F

2

F

1

C

1

C

2

C

3

C

4

C

5

C

6

M

1

BL

DP

H

LS

F

2

Start

+24 V DC

+24 V DC

0 V

PLC

Q1.1 Q1.2 Q1.3 Q1.4 Q1.5 Q1.6 Q3.0 Q4.1 Q4.2 Q5.0

I0.0

I1.0

I2.0

I2.1

I7.1

I7.2

I7.3

Inputs

Outputs

(a)

(b)

(c)

0 V