How SSR can be driven by analog?

[Lancie1]

The manual says 20 sec for relay output and 2 sec for SSR output. Makes sense.

Yes, the shorter the period, the better for accuracy. But with a relay, short times wear out the contacts very quickly, so there is a trade-off.

 

[danw]

do most temperature controllers give me a parameter where I can enter the total time range of time?

In general, yes.

As an example, Honeywell's UDCs controllers tell you this:

Time Proportional control with a single output is called Time Simplex:

the type of relay is defined, electromechanical or solid state:

The cycle time is specified:

 

[unsaint32]

This had been great education. Thanks for all your answers.

 

[unsaint32]

It occured to me... then if a SSR input is an analog input (say 4-20ma) then how does the SSR control output period changes when I cannot specify the output's total period? (like I set 20 seconds for relay output of a temp controller)

 

[paulcs]

If an SSR accepts an analog input, the literature will tell you the time duration. It might be something like one of these:

1) 4-20mA analog input, burst firing: "Overall cycle time = 0.5 seconds. Example: 12 mA = 50% = 0.25 seconds ON, 0.25 OFF, 0.25 ON, 0.25 OFF."

2) 4-20mA analog input, phase angle: "Delayed turn ON inside the sine wave. 8 mA = 25% = delayed start until 25% into the sine wave, then ON until the zero mark, delay 25%, then ON until the zero mark, etc"

3) 0-10 V analog input, half sine wave burst firing. 3.3 Volt = 33% = half a sine wave ON, then 2 half sine waves OFF.

Options 1 and 3 above are zero crossing so they are electrically noise free. Option 2 is phase angle. It provides very good control but generates electronic noise that may be an issue especially in CE installations in Europe. Phase angle is typical for transformer coupled loads. Zero crossing is typical for resistive loads (most heaters). The half sine wave burst firing is for very fast loads such as IR heaters, etc.

 

[unsaint32]

Thanks paulcs. so, is that pretty much the convention for all SSRs with analog input?