Datasheet
13
®
XTR112, XTR114
TABLE IV. Error Calculation.
SAMPLE ERROR CALCULATION FOR XTR112
(1)
RTD value at 4mA Output (R
RTD MIN
) 1000Ω
RTD Measurement Range 200°C
Ambient Temperature Range (∆T
A
)20°C
Supply Voltage Change (∆V+) 5V
Common-Mode Voltage Change (∆CM) 0.1V
SAMPLE
ERROR SOURCE ERROR EQUATION ERROR CALCULATION
(2)
UNADJ. ADJUST.
INPUT
Input Offset Voltage V
OS
/(V
IN MAX
) • 10
6
100µV/(250µA • 3.8Ω/°C • 200°C) • 10
6
526 0
vs Common-Mode CMRR • ∆CM/(V
IN MAX
) • 10
6
50µV/V • 0.1V/(250µA • 3.8Ω/°C • 200°C) • 10
6
26 26
Input Bias Current I
B
/I
REF
• 10
6
0.025µA/250µA • 10
6
100 0
Input Offset Current I
OS
• R
RTD MIN
/(V
IN MAX
) • 10
6
3nA • 1000Ω/(250µA • 3.8Ω/°C • 200°C) • 10
6
16 0
Total Input Error: 668 26
EXCITATION
Current Reference Accuracy I
REF
Accuracy (%)/100% • 10
6
0.2%/100% • 10
6
2000 0
vs Supply (I
REF
vs V+) • ∆V+ 25ppm/V • 5V 125 125
Current Reference Matching I
REF
Matching (%)/100% • I
REF
• 0.1%/100% • 250µA • 1000Ω/(250µA • 3.8Ω/°C • 200°C) • 10
6
1316 0
R
RTD MIN
/(V
IN MAX
) • 10
6
vs Supply (I
REF
matching vs V+) • ∆V+ • 10ppm/V • 5V • 250µA • 1000Ω/(250µA • 3.8Ω/°C • 200°C) 66 66
R
RTD MIN
/(V
IN MAX
)
Total Excitation Error: 3507 191
GAIN
Span Span Error (%)/100% • 10
6
0.2%/100% • 10
6
2000 0
Nonlinearity Nonlinearity (%)/100% • 10
6
0.01%/100% • 10
6
100 100
Total Gain Error: 2100 100
OUTPUT
Zero Output (I
ZERO
- 4mA) /16000µA • 10
6
25µA/16000µA • 10
6
1563 0
vs Supply (I
ZERO
vs V+) • ∆V+/16000µA • 10
6
0.2µA/V • 5V/16000µA • 10
6
63 63
Total Output Error: 1626 63
DRIFT (∆T
A
= 20
°
C)
Input Offset Voltage Drift • ∆T
A
/(V
IN MAX
) • 10
6
1.5µV/°C • 20°C/(250µA • 3.8Ω/°C • 200°C) • 10
6
158 158
Input Bias Current (typical) Drift • ∆T
A
/I
REF
• 10
6
20pA/°C • 20°C/250µA • 10
6
22
Input Offset Current (typical) Drift • ∆T
A
• R
RTD MIN
/(V
IN MAX
) • 10
6
5pA/°C • 20°C • 1000Ω/(250µA • 3.8Ω/°C • 200°C) • 10
6
0.5 0.5
Current Reference Accuracy Drift • ∆T
A
35ppm/°C • 20°C 700 700
Current Reference Matching Drift • ∆T
A
• I
REF
• R
RTD MIN
/(V
IN MAX
) 15ppm/°C • 20°C • 250µA • 1000Ω/(250µA • 3.8Ω/°C • 200°C) 395 395
Span Drift • ∆T
A
25ppm/°C • 20°C 500 500
Zero Output Drift • ∆T
A
/16000µA • 10
6
0.5µA/°C • 20°C/16000µA • 10
6
626 626
Total Drift Error: 2382 2382
NOISE (0.1Hz to 10Hz, typ)
Input Offset Voltage v
n
/(V
IN MAX
) • 10
6
0.6µV/(250µA • 3.8Ω/°C • 200°C) • 10
6
33
Current Reference I
REF
Noise • R
RTD MIN
/(V
IN MAX
) • 10
6
3nA • 1000Ω/(250µA • 3.8Ω/°C • 200°C) • 10
6
16 16
Zero Output I
ZERO
Noise/16000µA • 10
6
0.03µA/16000µA • 10
6
22
Total Noise Error: 21 21
TOTAL ERROR: 10304 2783
(1.03%) (0.28%)
NOTES: (1) For XTR114, I
REF
= 100µA. Total unadjusted error is 1.16%, adjusted error 0.31%. (2) All errors are min/max and referred to input, unless
otherwise stated.
ERROR
(ppm of Full Scale)
REVERSE-VOLTAGE PROTECTION
The XTR112’s and XTR114’s low compliance rating (7.5V)
permits the use of various voltage protection methods with-
out compromising operating range. Figure 4 shows a diode
bridge circuit which allows normal operation even when the
voltage connection lines are reversed. The bridge causes a
two diode drop (approximately 1.4V) loss in loop supply
voltage. This results in a compliance voltage of approxi-
mately 9V—satisfactory for most applications. If 1.4V drop
in loop supply is too much, a diode can be inserted in series
with the loop supply voltage and the V+ pin. This protects
against reverse output connection lines with only a 0.7V loss
in loop supply voltage.
SURGE PROTECTION
Remote connections to current transmitters can sometimes be
subjected to voltage surges. It is prudent to limit the maximum
surge voltage applied to the XTR to as low as practical.
Various zener diode and surge clamping diodes are specially
designed for this purpose. Select a clamp diode with as low a
voltage rating as possible for best protection. For example, a
36V protection diode will assure proper transmitter operation
at normal loop voltages, yet will provide an appropriate level
of protection against voltage surges. Characterization tests on
three production lots showed no damage to the XTR112 or
XTR114 within loop supply voltages up to 65V.