Model 7421 | Multifunction Analog/Digital I/O

Model 7421 Multifunction Analog/Digital I/O
  • 3 quadrature encoder channels with 16-bit counters
  • Four 12-bit D/A outputs
  • Eight 12-bit differential A/D inputs
  • Watchdog timer
  • 24 bi-directional digital signals

Model 7421 is obsolete. This archived information is provided as a courtesy to customers who own model 7421 units.


Sensoray's model 7421 is a low cost interface that saves space in STD bus systems by combining five functions into one module. Four flat cables connect the Model 7421 to external breakout boards.

Model 7421 Analog and Digital Interface



Three 16-bit up/down counter channels are optimized for incremental encoders. Each channel accepts two phased TTL or RS-422 signals to track encoder direction and displacement. Unlike conventional counters, the 7421 counters do not accumulate errors when the encoder dithers or changes direction. The 7421 supplies 5-volt power to each encoder channel.


Eight differential input channels are multiplexed to a sample/hold and successive approximation A/D. A resistor-programmable instrumentation amplifier allows gains of 1 to 1000. The 15-volt outputs from the DC/DC supply ensure A/D linearity for 10 volt input signals.


Four voltage output channels may be programmed for 0 to +10 volts. One channel has a remote sense input to minimize line loss errors. All output voltages are reset to zero volts whenever a bus reset occurs.

Watchdog timer

The 7421's watchdog timer output may be routed to either bus reset or nonmaskable interrupt. It may be enabled or disabled under program control. The timer is automatically disabled whenever a bus reset occurs.

Digital I/O

The Model 7421 has twenty-four digital I/O lines with industry standard pinouts for solid state relay boards. Each line is software programmable as an input or output. The status of output lines may be monitored by software. Whenever a system reset occurs all output channels are turned off.


Input resistance100 MΩ
Maximum input voltage63 VAC rms
CMMR95 db/min
Maximum command mode±5 V
A/D converter16-bit integrating
Conversion time22 ms/channel
A/D scan rate45 samples/second
Operating temperature-25 to 85 °C
InterfaceSTD 80
Input power5 V at 100 mA
Dimensions(W x H x D): 4.50 x 6.50 x .378 inches
Sensor Types
ThermocouplesJ, K, T, S, E, B, N, C, R
Platinum RTD100 Ω, types 385 and 392
Nickel RTD120, 200, 1000 Ω
Copper10 Ω
Thermistors10000 Ω, YSI type 44006 or 44031
Strain gauges120 to 4000 Ω
Sensor Resolution Range
Thermocouples 0.1 °C -270 to 1760 °C
Thermistors 0.01 °C -55 to 145 °C
Resistors 0.02 Ω
0.125 Ω
31 Ω
0 to 400 Ω
0 to 3 kΩ
0 to 600 kΩ
RTDs 0.05 °C
0.0125 °C
-200 to 800 °C
0 to 400 °C
Strain/pressure 5 µV ±100 mV
DC voltage 5 µV
20 µV
200 µV
±100 mV
±500 mV
±5 V


File Version Type Size
Model 7421 Instruction Manual1.0.0PDF150 KB

Pricing & Ordering

Model Description Qty 1 Qty 2-9 Order Qty.
7421Multifunction Analog/Digital I/OCallCall 
Relay boards
720RBSolid State Relay BoardCallCall 
720RBDINSolid State Relay Board, DIN rail mountableCallCall 
Breakout boards
7502TDINBreakout board, 20-pin, DIN rail mountable$50$50
7505TDINBreakout board, 50-pin, DIN rail mountable$81$74
7506TDINBreakout board, 40-pin, DIN rail mountable$80$73
7501CCable, flat, 50 conductor, 18 inches$18$16
7502CCable, flat, 20 conductor, 18 inches$13$12
7502C1Cable, flat, 20 conductor, 1 meter$26$24
7409CCable, flat, 40 conductor, 18 inches$20$19
7409C1Cable, flat, 40 conductor, 1 meter$29$26
7501C1Cable, flat, 50 conductor, 1 meter$31$28

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