user53372: I'm not very advanced in Arduino "core" functions, so I need your help.
I'm using a Solid State Relay in order to control a heating element, with a PID Library (PID_v1.h) to obtain the OUTPUT of the PWM.
The code itself is not a problem, so that I'll not post it here. 
Summarizing, this is the code where I send the PWM to the Relay:
    analogWrite(RELAY_OUT, outputValue);
I've found in this article that:
"The analogWrite function is used to set the duty cycle of a PWM pulse train that operates at approximately 500 Hz. Thus, with a frequency = 500 Hz, the period is = 2 ms."
My concern is that the response time of the relay (FOTEK SSR-60 DA) is 10ms (to turn on or to turn off), but I DO NOT KNOW how to configure Arduino PWM to work accordingly to this Relay, in a period greater than 10ms.
I've found in some pages some people changing the clock frequency in order to have a "fast pwm", but I need to know what values I have to use to get a "slow pwm", for a period greater then 10ms.
Can you help me with that? I've been searching a lot for this answer, but I could not find any "definitive"answer.
Thank you in advance!
Everton

user2881: I'd suggest using the TimerOne library. 
Call Timer1.initialize(10000) in setup. 
Then call Timer1.pwm(pin, duty); in your loop. Where pin is 11, 12, or 13 for the MEGA, and duty is between 0 and 1023.

53372: <p>I'm not very advanced in Arduino "core" functions, so I need your help.</p>

<p>I'm using a Solid State Relay in order to control a heating element, with a PID Library (PID_v1.h) to obtain the OUTPUT of the PWM.</p>

<p>The code itself is not a problem, so that I'll not post it here. </p>

<p>Summarizing, this is the code where I send the PWM to the Relay:
    analogWrite(RELAY_OUT, outputValue);</p>

<p>I've found in this <a href="http://web.cecs.pdx.edu/~gerry/class/EAS199A/topics/pdf/PWM_output_Arduino.pdf" rel="nofollow noreferrer">article</a> that:
"The analogWrite function is used to set the duty cycle of a PWM pulse train that operates at approximately 500 Hz. Thus, with a frequency = 500 Hz, the period is = 2 ms."</p>

<p>My concern is that the response time of the relay (FOTEK SSR-60 DA) is 10ms (to turn on or to turn off), but I DO NOT KNOW how to configure Arduino PWM to work accordingly to this Relay, in a period greater than 10ms.</p>

<p>I've found in some pages some people changing the clock frequency in order to have a "fast pwm", but I need to know what values I have to use to get a "slow pwm", for a period greater then 10ms.</p>

<p>Can you help me with that? I've been searching a lot for this answer, but I could not find any "definitive"answer.</p>

<p>Thank you in advance!</p>

<p>Everton</p>
 2881: <p>I'd suggest using the <a href="https://github.com/PaulStoffregen/TimerOne" rel="nofollow noreferrer">TimerOne library</a>. </p>

<p>Call <code>Timer1.initialize(10000)</code> in <code>setup</code>. 
Then call <code>Timer1.pwm(pin, duty);</code> in your loop. Where <code>pin</code> is 11, 12, or 13 for the MEGA, and <code>duty</code> is between 0 and 1023.</p>
