PXIe-2527 Daughterboard
- Updated2024-07-08
- 4 minute(s) read
PXIe-2527 Daughterboard
The PXIe-2527 daughterboard contains 38 relays. 32 relays are channel relays that control which channels are selected. These relays, connected to the front panel, control the channels and temperature sensing circuitry (housed in the accompanying terminal block) by switching them on or off. The other 6 relays are configuration relays, with 3 of them connected to the front panel to route the signals for COM0, COM1 and CJTEMP. The 32 channel relays route input signals to the 6 configuration relays.
The front connector is a 100-pin right-angle HDI connector that provides the necessary pin density and creepage & clearance requirements. The relay drivers used on the PXIe-2527 are octal D flip-flops.
Complex Programmable Logic Device (CPLD)
The CPLD on the PXIe-2527 transports the serial data stream from the motherboard and runs the data stream through a shift register. This behavior creates a 24-bit wide parallel data stream. The 24-bit array consists of 16 data bits and 8 address bits. The 16 data bits are least significant bits (LSBs) and the 8 address bits are most significant bits (MSBs). The address specifies the bank that the CPLD wants to communicate with, while the 16 data bits represent the data that is written to each of the 8 relays within that bank.
Relay
Operation
The PXIe-2527 uses single-coil latching relays. When you apply a positive voltage across the set polarity of the coil, the relay operates to the set position if it is not already there. Once the relay contacts reach the set position, the drive voltage can be removed and the relay contacts stay in the same position until a voltage of the opposite polarity is applied to the coil. To open or close a relay, you can apply a voltage of one polarity or the other across the relay coils.
Relay
Configuration
The following list describes the 6 configuration relays on the PXIe-2527.
| Configuration Relay | Description |
|---|---|
| The KBC01 Relay | When set, this relay multiplexes all channels to COM0 for 1-wire and 2-wire mode. This relay is reset for 4-wire mode so half the channels are multiplexed to COM0 and the other half to COM1. |
| The CJTEMP Relay | When set, this relay connects COM0 to the temperature circuitry in the terminal block. When reset, this relay connects to the channels. |
| The KREF0 Relay | When set, this relay is used only in 1-wire mode to connect to a reference voltage. When reset, this relay connects to the channels. |
| The KREF1 Relay | This relay functions the same as the KREF0 relay which enables a dual, 16x1, 2-wire mode configuration. |
| The KHLSELECT0 Relay | When reset, this relay connects COM0 to channels 0-31 in 1-wire mode. When reset, it connects to channels 32-63 1-wire mode. |
| The KHLSELECT1 Relay | This relay functions the same as the KHLSELECT0 relay which
enables a dual 32x1 1-wire mode configuration. For 1-wire and 2-wire mode, only one channel relay is multiplexed to the COM at a time. For 4-wire mode, only one channel relay from Bank 0 and one channel relay from Bank 1 are set at a time. |
Isolated
Power Supply
The PXIe-2527 is designed for CAT I isolation at 300 V continuous and 1500 V impulse channel-to-channel and channel-to-ground. This design means the power lines and CPLD inputs from the motherboard must be isolated from the daughterboard.
The PXIe-2527 daughterboard gets all of the isolation from the power lines through two 1 W DC-DC converters providing 3000 V of isolation. One converter drives the CPLD, the 3.3 V regulator, other electronics, half the relay drivers, and half the relays. The second converter drives the other half of the relay drivers and relays. The output grounds of these converters are tied together and two diodes are placed between the 5 V outputs of the converters going in opposite directions. These diodes enable one converter to power the circuitry of the other converter for a short period of time during the power-up process. This occurs when one converter reaches a voltage of up to 5 V before the other converter.
The CPLD inputs coming from the motherboard have 2500 V of isolation through a quad digital isolator.
Terminal
Block Temperature Sensing Circuit
The TB-2627 terminal block for the PXIe-2527 uses a temperature sensing circuit. This circuit uses a 2.5 V voltage reference and a thermistor that reads 5 K ohms at 25 degrees Celsius. Issues with the voltage reference and the load resistor may cause temperature errors. Refer to the PXIe-2527 Specifications for calculating thermocouple error.
