Multifunction Controls in a Bench DAQ
2019-10-11 | 9 min read
What are multifunction controls in a bench DAQ? Most engineers who have used DAQ knows the many benefits and versatility of a bench data acquisition (DAQ) system. A DAQ has data logging capability that can measure and monitor temperature, voltage, current, resistance, and many more types of signals over long periods. A DAQ is also known to have switching modules that can multiplex many inputs into a single test instrument or a matrix of switches for complex array of testing. However, do you know that a bench DAQ can excite sensors and actuators, perform counting of events, and control test systems via digital I/O interface?
In this blog, I will share with you the capabilities and usefulness of the DAQM907A multifunction control module that is perfectly matched to the Keysight’s DAQ970A bench system. The multifunction module adds two additional measurement input capabilities to the DAQ system, which are the digital input and event totalizer. The multifunction module also contains a dual voltage output from its digital to analog converter (DAC).
Let us explore the capabilities of the multifunction module in a little more detail.
Digital Input/Output Control
The DAQM907A multifunction module has two non-isolated 8-bit digital input and output ports as shown in Figure 1. You can read the live status of the bits on the port, or you can configure a scan to include a digital read. Each port has a separate channel number on the module and contains 8-bits. You can combine the two ports to read a 16-bit word. Vice-versa, you can also use the ports to output digital patterns up to 16-bit word.
By having a digital input/output control, you can also assign alarms to port 1 and port 2 channels on the multifunction module. You can generate an alarm when a specific bit pattern or bit pattern change is detected on a digital input channel. With the multifunction module, the channels do not have to be part of the scan list to generate an alarm. Of course, it will be convenient to include the reading of the input ports for every scan, if necessary. You can then set a digital mask or a pattern where the test status is ‘Fail’ if not equal or equal to the set pattern.
You can also set the two ports as output ports. Each output bit is capable of directly driving up to 10 TTL loads. They are open-drain outputs and can sink up to 400 mA from an external power supply. Using an external power supply, you can use these output ports to drive solenoid-based actuators or switches that control say RF or Microwave signals or changing the state of your device under test, and more.
The DAQM907A multifunction module has a 26-bit totalizer, which can count pulses at a 100 kHz rate. You can manually read the totalizer count, or you can configure a scan to read the count.
The totalizer is a very useful feature where it can count events up to 67,108,863 (226-1). The count rolls over to "0" after reaching the maximum allowed value. You can configure the totalizer to count on the rising edge or falling edge of the input signal. Using the hardware jumper labeled "Totalize Threshold" on the module, you can control the threshold at which an edge is detected. Move the jumper to the "AC" position to detect changes through 0 volts. Move the jumper to the "TTL" position to detect changes through TTL threshold levels.
Figure 3 shows you the +/-IN the differential input signal and the Gate input terminals to enable and disable the counting.
Figure 4 shows a train of input pulse signals. The totalizer in the example will only count when the gate signal condition is ‘High’ and when the input signal is on a rising edge during the threshold crossover.
Applications using the totalizer can be as simple as counting the number of times an actuator switch, counting an optical encoder as the motor spins, number of times the sensor measurements have passed the threshold, or a handshaking event with another instrument or a signal from the device under test. Just like the digital input/output, you can set the alarm when a specific count is reached on a totalizer channel.
Analog Output (DAC)
The DAQM907A module has two ± 12 V analog outputs and senses capable of outputting calibrated voltages or currents with 18 bits of resolution. Each DAC channel can be used as a programmable voltage or current source for analog input to other devices. See Figure 5.
The DAC output sense channels will make a complementary (voltage or current) measurement based on the output mode of the corresponding DAC output channel:
- Channel 06 will make the measurement based on the output mode set on channel 04.
- Channel 07 will make the measurement based on the output mode set on channel 05.
If DAC output channel 04 is set to voltage mode, then the corresponding DAC sense channel 06 will measure current. If the output channel is set to current mode, the sense channel will measure voltage.
Applications using these two ± 12 V DAC outputs can be as simple as source and measure verifications and testing on some active or passive components. You can also use it to accurately bias certain active sensors and measure its output.
Summary of the Multifunction DAQ Module
The DAQM907A multifunction module is a great complement to the DAQ970A mainframe data acquisition system. It provides the extra digital input and output ports to help trigger the alarm when a specific bit pattern is detected on the digital input channel, or it can be used to trigger and control multiple solenoid-based actuators/switches. The multifunction module also has an event totalizer to help you get closed-loop feedback of your test system by counting events such as the number of actuations or switching, the number of spins of a motor, or the handshaking controls between the DAQ with another instrument or a signal from the device under test.
The multifunction module also comes two ± 12 V analog outputs that provide the DAQ the ability to do basic source and measure verifications and testing.
To learn more about the DAQM907A multifunction module and the DAQ970A system, please visit www.keysight.com/find/DAQ970A.