End of Stroke Position Switches Applications Data

Series and Parallel Connection

Calculation Examples

Parker's End of Stroke position switches may be connected inseries, to give an AND function; or in parallel, giving an OR function. The maximum number of switches which may be connected, in series or in parallel, depends on the external load requirements. Calculation of maximum numbers is described below. These show how to determine the number of switches (n)which may be connected in series or parallel for a given voltage supply and output loading. The examples use the following values:Supply voltage V
s 24VMin. voltage across the load V
L 18VLoad resistance R

Series Connection (AND Circuit)

L 360 Ω The number of position switches which may be connected in series is limited by two factors – voltage drop and available current.A voltage drop of approxi-mately 1.5 volts occurs across each switch, therefore the output voltage available at the load is reduced by 1.5V x the number of switches in series. In addition, each switch must supply the no- load current of all the other switches, as well as the load current, thus the sum of all the no-load currents, plus the external load current, must not exceed the current of a single switch. The maximum number of switches permissi- ble is determined by whichever approach results in a lower number. Output resistance R
a using standard connector2.2k Ω Therefore:Min. external load current I
L = V
L /R
L 50mAMax. switch load current I
m = 5 x V
s (see Specification, page 6)120mA

Example – for Series Connection

a. Voltage relationship isV
s – n x V
d ≥ V
L – V ) Therefore number of switchesn ≤
s L V
d (24 – 18)1.5 (I n ≤ Therefore maximum number of switches = 4b. Current relationship isI
m ≥ I
L + nI
o – I )

Parallel Connection (OR Circuit)

n ≤
m L There is no limit to the number of switches which may be connected in parallel, provided that isolating diodes are fitted externally to the output of each switch, as indicated.Where connectors with LEDindicators are used, external isolating diodes must be fitted to prevent all of the LEDs from illuminating when one switch is actuated.If external diodes are omitted,the number of switches is limited because each switch would have to drive the internal collector load of all other switches, as well as the external loads. I
o (120 – 50) n ≤ 10 Therefore maximum number of switches = 7Using the lower of the two results shown above, the maximumnumber of switches which can be connected in series is four.

Example – for Parallel Connection

If external diodes are fitted, the number of switches is limited only by the power supply. Where external diodes are not fitted, the following current formula applies.Current relationship isn + ≤ I V
s V
s R R
m a L Thereforen ≤

((((()))))

I V
s R
a m –n R
L V
s ≤

(((((

120 241000 –n

)))))

360 242.2 x 1000 ≤ 4.9Rounding down, the maximum number of switches which canbe connected in parallel = 4 (V
Parker Hannifin plc

Hydraulics

Cylinder DivisionWatford, Herts.

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