FREQ is an internal device that allows you to measure the frequency of a digital signal. Also integrates a pulse counter one way a first-order low-pass digital filter on the measure, a function of scaling and a duty cycle.

The main features of the device are:

• selectable frequency resolution between 100th and 1/1000th of a hertz.
• forehead measurement signal acquisition selectable between ascent and descent.
• low-pass digital filter of first-order on the adjustable time constant measurement.
• scaling of the measurement by means of three programmable coefficients.
• acquisition of the duty cycle of the signal to be measured (for signals with frequencies below to 150 Hz).
• availability of frequency, measurement and measurement value filtered.

In order to use the device you must declare it in the appropriate INTDEVICE section of the configuration unit.

;--------------------------------- 
; Internal device declaration 
;--------------------------------- 
INTDEVICE 
...
<device_name>  FREQ  TCamp  IntL

Where:

	Attention: All fields of the declaration are necessary and must be present on the same line. Set “X.X” or “X” If a resource is not available or cannot be used. Disable a resource means disable all functionality of the device using it.

The “antiglitch filter” block execute a digital filtering on the input signal for troubleshooting. It samples the input signal at regular intervals and determines the exit status by checking the status of the majority of the samples. The size of the filter depends on a parameter of the QMOVE system (“QMOVE:sys004” system variable).

	The existence of the “antiglitch filter” block and it's features depend on the product that you are using. Consult the documentation relating to the product for more information.

The “edge detect” block capture the output signal from the antiglitch filter and measuring the time between two consecutive fronts to get the frequency measurement. The rising or falling is selected using capture parameter. The frqmin parameter determines the maximum time after which the block value becomes zero.

The “Edge counter” block creates a counter of faces captured by “edge detect” block.

Il blocco “Upper limiter”, come dice la parola stessa, limita i valori di uscita del blocco “edge detect” fino a frqmax.

The “scaling” block execute mathematical operations of multiplication, division and sum, of the block output “upper limiter” value with the scaleA, scaleB and scaleC parameters to get the value measured (outUm) in the desired entity.
The formula to get the measured value is:
outUm = (outbit * scaleA / scaleB) + scaleC

The “Low pass filter” block execute a digital filter of the first order (type of the classic RC filter) on the measured value. The time constant of the filter can be set using tfilter parameter.

• Antiglitch filter has a facility to remove any disturbances on the input signal but it has the disadvantage of introducing a “noise” on the output signal. This noise is more evident when the input frequency is higher than 10KHz. In these cases, you can reduce the noise considerably, until you cancel it, simply by increasing the sampling time of the device. If the application permits, we recommend using sampling times equal to or greater than 20ms.
• The device cannot function simultaneously as a frequency meter and duty cycle detector therefore, when the capture parameter is set to 5, the output value of the “edge detect” block represents the duty cycle expressed in parts per 10000 (5000 means duty of the 50.00%). The output value of the “edge detect” block goes directly to the outfrq parameter bypassing the “upper limiter” block; the “scaling” block produce outputs which could lose meaning. To use the filter of the first order with the duty cycle properly requires that the scaleA and scaleB parameters are equal to 1 and the scaleC parameter is equal to zero. Using the transmitter duty cycle works fine for low frequency signals (less than about 150 Hz).

When the device fails to perform operations are caused by incorrect programming by the user reports this condition through activation of the st_error state. The device, also, makes available, through the values information errcode and errvalue parameter, some information for a better understanding of the type of error and what condition the generated. This information and the error state st_error, continue until you run the appropriate RSERR command that will remove them.
The following table specifies the values assumed by errcode:

Through the errvalue parameter you can get more detailed information about the error.
The following table specifies the values assumed by errvalue:

When the parameters of the device are programmed with out-of-range values they are not accepted and maintain their previous value. The device reports this condition through activation of the st_warning state. The device also provides, through the values parameter information wrncode andwrnvalue, some information to better understand the type of warning and what condition the generated. This information and the status of warning st_warning, continue until you run the appropriate RSWRN command that will remove them.
The following table specifies the values assumed by wrncode:

Through the wrnvalue parameter you can get more detailed information about the warning.
The following table specifies the values assumed by wrnvalue: