UAP1072 - USC Application

This application controlled flow by measuring frequency from a flow sensor, as there was a large amount of turbulence in the pipe large variations in flow were displayed. This problem was attacked in two ways;

1. Ensure that fluctuations in the readings were due to flow variations and not noise.
2. Filtering of the measured flow for a clearer display. The PID control did not include the filter in the control loop.

Specific Correction Methods

• When measuring frequency on the pulse inputs there is no facility to filter the input. This application filters the measured frequency using a similar technique to UAP0024 and the PID algorithm in UAP0040.
• The pulse input gives a new reading every 70mS as long as the input frequency is greater than 14.5Hz. The pulse input will work up to 5kHz, therefore high frequency noise on top of a low frequency signal cause jitter.
• If a open collector sensor with a 10k ohm pull up were used and the maximum rate were 300Hz a 33nF capacitor would cause a 50% reduction of signal at 600Hz removing the possibility of noise in most cases.
• Also as the input circuit has a 22k dropping resistor internally the signal would in the example above switch between 0 and 3.4V. Setting the input switching point to 1.7V would give the maximum immunity.
• This application uses signal limiting on the output, as the trim menu on the output overwrites the signal limiting trim menu on the output has been disabled.

Hot keys

	KEY	Display
	UP	Input speed (P1)
	DOWN	Setpoint
	BACK	PID out% in auto mode or %out in manual mode
	NEXT	P1 Filtered
	ENTER	Trim menu.

Scaleing

ScaleMin = Minimum usable input range (0)
ScaleMax = Minimum usable output range (250)

PID Tuning

1. If ScaleMin or ScaleMax are changed then PID will need re-tuning
2. First try set PB% = 200, I time S = 900, D time S = 0
3. Run plant and reduce PB% until control oscillates or increase until control stops osculating.
4. Once the value for PB% is found where control is on the edge of oscillation then reduce by about 5%.
5. Reduce 'I time S' until process controls around or close to set point. Do NOT make 'I time S' = 0.
6. Set 'D time S' to approximately where 'I time S' = I and 'D time S' = D.

Issue	Comment
	If unexpected results occur when loading the .usc file press back and click Help for instructions.
a	uap1072a.usc = USC application program. uap1072a.pdf = printable copy of application with comments on program listing.
b	Add auto manual control and hot keys. uap1072b.usc = USC application program. uap1072b.pdf = printable copy of this page.