RTD measurement accuracy. Omega OM-USB-TEMP

OM-USB-TEMP User's Guide Specifications

Note 12:

Note 13:

Resistance values greater than 180 k ohms cannot be measured by the OM-USB-TEMP in the thermistor mode. The 180 k ohm resistance limit includes the total resistance across the current excitation (±Ix) pins, which is the sum of the thermistor resistance and the lead resistances.

For accurate three wire compensation, the individual lead resistances connected to the ±Ix pins must be of equal value.

Throughput rate

Table 9. Throughput rate specifications

Number of Input Channels

7

8

5

6

3

4

1

2

Maximum Throughput

2 Samples/second

2 S/s on each channel, 4 S/s total

2 S/s on each channel, 6 S/s total

2 S/s on each channel, 8 S/s total

2 S/s on each channel, 10 S/s total

2 S/s on each channel, 12 S/s total

2 S/s on each channel, 14 S/s total

2 S/s on each channel, 16 S/s total

Note 14: The analog inputs are configured to run continuously. Each channel is sampled twice per second.

The maximum latency between when a sample is acquired and the temperature data is provided by the USB unit is approximately 0.5 seconds.

Digital input/output

Table 10. Digital input/output specifications

Digital type

Number of I/O

Configuration

Pull-up/pull-down configuration

Digital I/O transfer rate (software paced)

Input high voltage

Input low voltage

Output low voltage (IOL = 2.5 mA)

Output high voltage (IOH = –2.5 mA)

CMOS

8 (DIO0 through DIO7)

Independently configured for input or output.

Power on reset is input mode.

All pins pulled up to +5 V via 47 K resistors (default). Pull-down to ground

(GND) also available.

Digital input – 50 port reads or single bit reads per second typ.

Digital output – 100 port writes or single bit writes per second typ.

2.0 V min., 5.5 V absolute max.

0.8 V max., –0.5 V absolute min.

0.7 V max.

3.8 V min.

Note 15: All ground pins on the OM-USB-TEMP (pins 9, 19, 28, 38) are common and are isolated from earth ground. If a connection is made to earth ground when using digital I/O and conductive thermocouples, the thermocouples are no longer isolated. In this case, thermocouples must not be connected to any conductive surfaces that may be referenced to earth ground.

Memory

EEPROM

Table 11. Memory specifications

1,024 bytes isolated micro reserved for sensor configuration

256 bytes USB micro for external application use

Microcontroller

Type

Table 12. Microcontroller specifications

Two high-performance 8-bit RISC microcontrollers

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