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Isolated/Stackable DAQ Module HMI SCADA Software
 

Isolated Stackable DAQ
Modules with Free Software

We offer a full line of low-cost Data Acquisition and Control modules which can be daisy chained together and connected to a single communications port of a PC or Laptop. Because these modules are stackable, allows the user to select any combination of features needed for their application, and to expand with additional features when necessary. Our Data Collection Software as pictured above is specifically designed to communicate with these DAQ modules and can be set up very quickly and easily by the novice using little or no programming skills. For more advanced programs with special requirements, our engineers can put together a custom software application for you. This can include the mapping of all of the data points to individual cells in your Excel Spreadsheet which will update automatically.

 

Frequency Measurement Cards

Frequency Counter Card Pulse Counter/Timer Card WTPCT-M
Read the Frequency of an input signal from 0.50000 Hz to 1,400,000 Hz using 5 digit resolution throughout the entire range. Can also read RPM, Period, or Duty Cycle. read more...

 

Frequency Counter Definition

To measure the frequency of an alternating current electrical signal, a counter is used to count the number of wave form cycles that occur over a given time period. The frequency can then be determined by using the formula: frequency = count / time. This method works fine for high frequency signals because the count will end up being a large number over a short sampling period which allows for high resolution results from the formula mentioned above. Unfortunately, if measuring a low frequency signal, the instrument would have to sample the signal for a very long time period to get the same kind of precision. Unlike most frequency counters which merely count the number of cycles that occur over an exact predetermined gated time-period, the WTPCT-M shown here not only counts the cycles, but measures the exact time it takes for a significant number of cycles to complete by starting the gate precisely at the leading edge of the first cycle, and stopping the gate precisely at the trailing edge of the last cycle. This method greatly increases the precision, and resolutions of .00001 Hz can be achieved at the low end of the frequency spectrum. The number of cycles sampled is continuously variable and is determined by the input frequency.

Stackable Capability

Stackable refers to the ability to connect multiple units together and share a single communications port of a host PC, laptop, or Single Board Computer (SBC). The communications bus uses a stratagem based on the Carrier Sense Multiple Access (CSMA/CD) protocol. Carrier Sense (CS) is the monitoring of the data bus for a period of inactivity before a DAQ module is allowed to begin its own transmission. Multiple Access (MA) means that once the bus is free, every DAQ module in the network has an equal opportunity to transmit a frame. And Collision Detection (CD) uses non destructive bit wise arbitration to preserve the integrity of a data frame when two or more DAQ modules try to transmit at the exact same time. And since the data frame that wins arbitration remains intact during a collision, there is no additional communications delay when a collision occurs no matter how often it happens.

Host Communications

To communicate with the DAQ modules, commands are sent to the individual units by including a header character at the beginning (the address) so that it can be routed to the appropriate unit. If using multiple units connected together, the DIP switch for each unit should be set to a different position so that it will be assigned a different header character. Each DAQ module has its own command set used to configure it, operate the functions, and to read data from it. These commands are listed in the product data sheets. A typical command string looks like this:

HCNV{cr}

H = Header Character
C = Command Character
N = Channel Number (if applicable)
V = Value (if applicable)
{cr} = Carriage Return

If using our ModCom HMI software, the carriage return is not necessary because ModCom automatically inserts this at the end of each command string. ModCom has a communications dialog box which can be used to transmit individual commands to the DAQ modules and see the data coming back. This is helpful in learning the style of the command-set protocol and testing the hardware that's attached to the DAQ module. It is highly recommended that this testing be done prior to setting up any complex control programs.