Delta Electronics Programmable Logic Controller DVP-PLC - Manual (Page 9)

1 Basic Principles of PLC Ladder Diagram
DVP-PLC Application Manual 1-5
Internal relay
The internal relay does not have connection with the external. It is an auxiliary relay inside the
PLC with the functions same as those of the auxiliary (middle) relay in the electric control
circuit. Every internal relay corresponds to a basic internal storage unit and can be driven by
the contacts of the input relay, contacts of the output relay and the contacts of other internal
devices. There are no limitations on the times of using the contacts of the internal relay and
there will be no output from the internal relay, but from the output point.
& Device indication: M0, M1,…, M4095 are indicated as M and numbered in decimal form.
Step
DVP series PLC offers a step-type control program input method. STL instruction controls the
transfer of step S, which makes it easy for the writing of the control program. If you do not use
any step program in the control program, step S can be used as a internal relay M as well as an
alarm point.
& Device indication: S0, S1,…S1023 are indicated as S and numbered in decimal form.
Timer
The timer is used for timing and has coil, contact and register in it. When the coil is On and the
estimated time is reached, its contact will be enabled (contact A closed, contact B open). Every
timer has its fixed timing period (unit: 1ms/10ms/100ms). Once the coil is Off, the contact iwlwl
be disabled (contact A open, contact B closed) and the present value on the timer will become
“0”.
& Device indication: T0, T1,…,T255 are indicated as T and numbered in decimal form.
Different No. refers to different timing period.
Counter
The counter is used for counting. Before using the counter, you have to give the counter a set
value (i.e. the number of pulses for counting). There are coil, contact and registers in the
counter. When the coil goes from Off to On, the counter will regard it as an input of 1 pulse and
the present value on the counter will plus “1”. We offer 16-bit and 32-bit high-speed counters
for our users.
& Device indication: C0, C1,…,C255 are indicated as C and numbered in decimal form.
Data register
Data processing and value operations always occur when the PLC conducts all kinds of
sequential control, timing and counting. The data register is used for storing the values or all
kinds of parameters. Every register is able to store a word (16-bit binary value). Double words
will occupy 2 adjacent data registers.
& Device indication: D0, D1,…,D9,999 are indicated as D and numbered in decimal form.