Applications
The Model Q498 can be used in many different types of operations. This section describes a few of the Process Control applications and how to configure the unit in order to perform the various operations.

Track & Hold
The Track & Hold function is easy to implement. The Digital Input is the control element. Simply short the Digital Input, Pin A6 to Digital Common, Pin A3. This can be accomplished via an external relay or switch. When the two terminals are connected together, the Analog Output will be held at the current output level until the connection is opened. Because the system is under microprocessor control, when the digital input is grounded, the current output level that is being processed, cannot be stopped. As an extreme example, if the output has been told to make a step change from 0V to 10V, the output could still be in the process of slewing to that value, (which could take as long as 700mSec). When the Hold input is applied, during that 700mSec window, the output will continue to rise to the 10V level and then hold at that point. The Hold function only stops any future input changes from having any effect on the output.

If a step response is not desired when the Hold line is released, ensure that the Output Changing Limit is set to the desired amount, in the Configuration Window section of the C698 Configuration Software.

HI/LO Select
This function is accomplished by selecting either the Max or Min function for F1(x). (Refer to the Output Math section of the Specifications.) After F1(x) has been assigned the Max or Min function, the higher input, (or lower if Min is selected) will drive the output. If a step response is not desired when the input channels switch control, then ensure the Output Changing Limit (accessed in the Configuration window of the configuration software) is set to the desired amount. Take note that the coefficients A and B and the exponents of each channel also effect the comparison.

The digital output can be programmed to go high when CH1>CH2, or when CH1<CH2. The Yellow LED indicates the status of the digital output.

Totalization/Integration
The Q498 is useful in totalizing applications, where the total number of pulses counted in a given time period represents the time integral of the DC input. If, for example, the input represents a flow in gallons per hour, then the time integral of this flow signal (total count) will represent total gallons.

This application requires two units in order to accomplish both functions. For example, the first Q498 might receive a frequency input from a turbine flow meter and convert it to a 0-10V level. That signal, along with a 0-10V signal representing say differential temperature are fed into the analog inputs of the second Q498 and added together produce a 0-10V level that could represent BTU/Minute, which would be fed into possibly a chart recorder. That same signal is also fed back to the analog input of the first Q498 and now used as a DC to frequency converter to produce a signal that can be fed to a counter to represent total BTU. Visit the Applications section of our website, www.actionio.com for a complete description and application diagram.

25-Point Linearization
The Q498 provides the ability for the user to input unique linearization tables. This feature is only available through the C698 software package, and can only be used on analog input 1 (Ch 1).

Digital Output And Frequency Output Loads
The frequency and digital outputs are designed to be powered with a 24VDC external supply. These outputs will each safely sink a maximum of 20mA. If an external supply is not used, the digital and frequency outputs are limited to 1mA.

Math Functions
All of the basic math functions perform percentage math, not true math. The formulas are as follows:

PC Programmable
The Model Q498 is calibrated either via a serial port from a PC or by using the onboard DIP switch and pushbutton. Math Functions and Process Control Functions are only configurable using the optional PC Configuration Software Model C698.

Touchcal Technology
Low-cost, microprocessor technology has enabled the replacement of zero and span adjustment potentiometers with push-button “Touch-CALTM” technology. Essentially, the thermal drift and mechanical variability of the potentiometers have been removed and replaced with a digitally stable circuit. Additionally, the inherent zero and span interactivity of potentiometer based analog amplifier circuitry is removed, providing 100% non-interactive adjustment.

The software comes with a serial cable to connect the Q498 to a serial port of a PC. The software is also available on our Website. The software is compatible with Windows 95, 98, 2000 and NT operating systems. The user instructions are included in the program as Help screens.

TouchCAL technology enables precise calibration and provides more than 90% offset of the zero value and adjustment down to 10% of the full scale input span for most of the six switch selectable input ranges. For example, the DIP switch set for ±25mA input range could be configured via the push button for an offset range of 4 to 20mA (58% offset and 68% span reduction) or –25 to 0mA (a 50% span reduction). If the output was configured for 0- 10V, then –25 to 0mA input would correspond to the 0-10V full scale output. Thus, input ranges such as 4-20mA or 0-5mA are possible using the ±25mA range.

Diagnostic LEDs
The Q498 has three diagnostic LED’s. The Green LED, labeled RUN, is used to indicate that power is on, and for diagnostics. It flashes quickly if the input signal is above the configured range or slowly if the input signal is below range. The RUN LED is continuously on when the unit is functioning within the configured range. The Red LED flashes when the output is over/under range. The Yellow LED indicates the status of the Discrete Output. The LED’s also provide indication of which steps are being performed during push button calibration.