Model: PCI‑6704

Part Number: 777306‑01 / 183689‑01

Brand: National Instruments (NI)

Type: 16-bit, 32-channel static analog output (16 channels of voltage + 16 channels of current) + 8 channels of DIO

Bus: Standard PCI (5 V, half-length card)

Connector: 1 × 68-pin SCSI (female)

Driver: NI‑DAQmx

Status: Out of Production (EOL), recommended replacement: PCIe‑6738NI

Core Overview

PCI‑6704 is an enhanced version of PCI‑6703, a software-synchronized (static) analog output card, providing 16 ±10 V voltage outputs + 16 0–20 mA current outputs, a total of 32 analog outputs, each channel with independent 16-bit precision, and integrated 8 5 V TTL/CMOS digital I/O. Suitable for industrial process control (4–20 mA loops), sensor calibration, valve/actuator drive, static setpoint control, etc.

Main Specifications

Analog Output (AO)

Channels: 16 voltage channels (VCH0–VCH15) + 16 current channels (ICH16–ICH31)

Resolution: 16 bits (for all channels)

Voltage range: ±10 V (default)

Accuracy: ±1 mV

Load: ≥1 kΩ; maximum ±10 mA

Current range: 0–20 mA (source current, no sink current)

Accuracy: ±2 μA

Load: ≤750 Ω (external power supply)

Stability time: typical 14.4 ms, maximum 48.8 ms

Temperature coefficient: 5 μV/°C (voltage offset), 1 ppm/°C (voltage gain)

Update mode: Software timing (static)

Scan period: 50 μs / channel

Digital I/O (DIO)

Channels: 8 bidirectional, 5 V TTL/CMOS

Input: Low ≤ 0.8 V; High ≥ 2.0 V

Output: Low ≤ 0.55 V @ 16 mA; High ≥ 2.4 V @ 16 mA

Power-on state: Input high impedance Power supply

+5 V @ 2.6 A

±12 V @ 70 mA (analog circuit)

Operating temperature: 0 ~ 55 °C

Features: Dual output of voltage/current, short circuit protection, user-defined power-on state, automatic calibration Typical application

Industrial 4–20 mA loop control (transmitter, valve, actuator)

Sensor calibration source (voltage/current reference)

Process setpoint control (temperature, pressure, flow)

Relay/contactor drive, analog load

ATE static test, DAC simulation, closed-loop control

PCI‑6704 User Manual (Chinese Version - Simplified Operation)

1. Hardware Installation

Power off: Shut down the PC and unplug the power cord.

Insert card: Insert PCI‑6704 into the 5 V PCI slot and tighten the retaining screw.

Wiring:

Use SH68‑68‑D1/E1 shielded cable to connect to the 68-pin SCSI port

Voltage output: VCH0–VCH15 (±10 V, single-ended)

Current output: ICH16–ICH31 (0–20 mA, source current)

DIO: D0–D7 (bidirectional 5 V TTL)

Power / Ground: +5 V, ±12 V, GND (connector auxiliary power supply)

2. Drive and Software Installation

Install NI‑DAQmx (required, supports Win7/10/11)

Open NI MAX:

Devices and Interfaces → Find PCI‑6704

Right-click self-check, display "Passed" for normal operation

Development Environment: LabVIEW, C/C++, Python, VB (DAQmx API)

3. Analog Output Configuration (DAQmx)

Mode: Static voltage/current output (software timing)

Voltage range: Fixed ±10 V

Current range: Fixed 0–20 mA (only source current)

Power-on state: Can be set to 0 V/0 mA, ±10 V, open circuit

Load requirements

Voltage: ≥1 kΩ, avoid voltage drop

Current: ≤750 Ω, external circuit power supply

Protection: Output short circuit automatic current limiting, overheat protection

4. Digital I/O Operations

Direction: Set input/output by byte

Read/write: Static read/write (no handshake)

Power-on: Default input open circuit, prevent false triggering

5. Key Considerations

Non-high-speed card: No hardware clock, no waveform generation; suitable for slow, stable output

Current output: Only source current, cannot absorb current; load ≤750 Ω

Common ground: Load and card share common ground, reduces noise

Channel crosstalk: Low in slow mode; shielded lines required for fast switching

Out of production: New design recommendations use PCIe‑6738 (32 channels, 1 MS/s) NI

6. Common Questions

Output incorrect: Check load matching, common ground, preheat for 30 minutes, calibration

No current output: Confirm external circuit power supply, load ≤750 Ω, correct wiring

Cannot find device: Swap 5 V PCI slot, reinstall DAQmx, refresh MAX

PCI‑6704 vs PCI‑6703 (Selection Overview) Table

Project PCI‑6704 PCI‑6703

Analog output 16 channels of voltage + 16 channels of current (32 channels) 16 channels of voltage

Current output 0–20 mA (source current) No

DIO 8 channels 8 channels

Power supply +5 V @2.6 A +5 V @1.5 A

Application Dual output of voltage + current (4–20 mA loop) Pure voltage control