ni272x Initialize Session VI
The ni272x Initialize Session VI opens a session to all channels on a single NI 272x device specified by the DAQmx Device Name parameter. Only one session per NI 272x device is permitted. Calling the ni272x Initialize Session VI multiple times invalidates previous sessions.
Connect and Disconnect Operations
ni272x Connect (Poly) VI
The ni272x Connect VIs allow multiple connection operations. The operations supported are:
- Connect two adjacent channels using the ni272x Connect 2Chan VI
- Connect two adjacent banks using the ni272x Connect 2Bank VI
- Connect a channel to the front panel test connector using the ni272x Connect to Connector 1Chan VI
Under most conditions, the ni272x Connect 2Chan VI should be used. The ni272x Connect 2Bank VI controls the hardware level banks, and should be used only if the low-level hardware configuration is thoroughly understood. The ni272x Connect 2Chan VI controls the software level channels. All NI 272x modules are composed of 8-bit banks. On 8-bit modules, each channel is composed of one bank. For example, channel 4 is composed of bank 4. On 16-bit modules, each channel is composed of two adjacent 8-bit banks. For example, channel 1 is composed of banks 2 and 3. Using the higher level channel calls abstracts the underlying architecture. Under most conditions, the ni272x Connect 2Chan VI should be used.
The ni272x Connect 2Chan VI addresses the software channels exposed to the user. For example, in the 16-bit example above, CH0 maps to banks 0 and 1, and CH1 maps to banks 2 and 3. Therefore, CH0+ maps to hardware bank1+, and CH1- maps to hardware bank2-. See the 272x device pinouts in the NI Switches Help for a complete listing of channel and bank connections.
The ni272x Connect 2Chan VI allows manual connection of adjacent software channels. For example, calling ni272x Connect 2Chan VI on a 16-bit module with channel N set to “0” and channel N + 1 set to “1” internally connects CH0+ to CH1-, creating two 16-bit resistors in series. These resistors could be used as a voltage divider or to create a dual N bit potentiometer. Multiple channels can be simultaneously connected. For example, connecting four channels together creates four series resistors, each of which is accessible via the front panel.
Similarly, the ni272x Connect to Connector 1Chan VI allows manual connection of channels to the front test connectors on your NI 272x module. The channels can connect to one of two channels: the "DUT Connector" or the "DMM Test Connector." The NI-272x Reference VIs only allow one channel to be simultaneously connected to the "DMM Test Connector."
Some NI 272x hardware topologies require an adjacent bank be disconnected from the "DUT Connector" before being utilized for connection to the "DMM Test Connector." The NI-272x Reference VIs will display an error if the required adjacent channel has been reserved for connection to a DUT. Likewise, operations on a reserved adjacent channel will fail until the selected channel has been disconnected from the "DMM Test Connector."
Caution: Be careful when using the ni272x Connect (Poly) VI with "ni272x Connector Identifier" set to "DMM Test Connector.” 8-bit modules require the reservation of an adjacent DUT channel, which causes the adjacent channel to be shunted to 0 Ohms in order to measure the channel under test. This may short out a DUT attached to the adjacent reserved channel. Therefore, NI recommends disconnecting the 37-pin DSUB connector on 8 bit modules before internally connecting channels to the DMM test connector.
ni272x Disconnect (Poly) VI
The ni272x Disconnect (Poly) VIs allow multiple disconnection operations. The operations supported are:
- Disconnect two channels using the ni272x Disconnect 2Chan VI
- Disconnect two banks using the ni272x Disconnect 2Bank VI
- Disconnect channel from front panel test connector using the ni272x Disconnect from Connector 1Chan VI
The ni272x Disconnect 2Bank VI controls the hardware level banks. The ni272x Disconnect 2Chan VI controls the software level channels by allowing manual disconnection of adjacent software channels.
Similarly, the ni272x Disconnect from Connector 1Chan VI allows manual disconnection of channels to the front test connectors on your NI 272x module.
ni272x Write (poly) VI
The ni272x Write (Poly) VI contains the following VIs:
ni272x Write Potentiometer 2Chan 1Samp VI
ni272x Write Resistance 1Chan 1Samp VI
ni272x Write Temperature 1Chan 1Samp VI
The ni272x Write Resistance 1Chan 1Samp VI and ni272x Write Temperature 1Chan 1Samp VI are used to set the corresponding resistance or temperature for each channel. Unit conversion VIs allow you to convert between resistance and temperature. For an example, see the block diagram of the ni272x Write Temperature 1Chan 1Samp VI.
The ni272x Write Potentiometer 2Chan 1Samp VI operates like a potentiometer. This VI connects channel N and channel N+1 together, sets channel N to closest channel N resistance, and sets channel N+1 to total potentiometer resistance minus coerced channel N resistance.
Note: Both legs of the potentiometer execute in parallel, so there’s a short period of time during relay settling when the physical resistance sum across both channels can be less than the user-defined total potentiometer resistance.
The ni272x Write Resistance 1Chan 1Samp VI determines and configures a coerced resistance value based on the requested resistance input for the device initialized in the ni272x Initialize Session VI. If you request a value that exceeds the maximum resistance of the device, error out returns an error. The coerced resistance displays the coerced output resistance available based the requested resistance values and the limitations of the initialized device.
The NI 272x modules use reed relays that settle over a period of milliseconds. During a resistance change, the driver outputs an intermediate resistance that is always higher than the requested value. Higher resistances are guaranteed on a single channel because the relays are always opened before they are closed. For example, if four relays in a bank are open and four relays are closed, calling the ni272x Write Resistance 1Chan 1Samp VI with an output that would require two relays to open and six relays to close will have an intermediate state where up to two additional relays are guaranteed to open before the additional relays close.
Note: This protection only exists per software channel. Connecting multiple channels with the ni272x Connect Channels VI and calling multiple ni272x Set Resistance VIs guarantees that the intermediate resistance on a given channel is higher than the current or final resistance.
The ni272x Write Temperature 1Chan 1Samp VI converts the requested temperature and Callendar-Van Dusen RTD parameters into a resistance. The VI outputs a resistance value based on the Requested Temperature, then calls the ni272x Write Resistance 1Chan 1Samp VI to set the resistance to the value outputted. Custom A, B and C Callendar-Van Dusen RTD parameters are required inputs. Values correspond to the physical characteristics of the RTD you wish to simulate.
ni272x Close Session VI
The ni272x Close Session VI allows you to close the session initialized by the ni272x Initialize Session VI.