Omega CYD201A Series User manual

Omega Model CYD201/202 User’s Manual
Table of Contents i
TABLE OF CONTENTS
Chapter/Paragraph Title Page
1 INTRODUCTION ..........................................................................1-1
1.0 General ..........................................................................1-1
1.1 Model CYD20X System Description...............................1-1
2 INSTALLATION ...........................................................................2-1
2.0 General ..........................................................................2-1
2.1 Inspection and Unpacking..............................................2-1
2.2 Repackaging For Shipment ...........................................2-1
2.3 Front and Rear Panel Definitions...................................2-2
2.3.1 Model CYD201 Definitions .........................................2-2
2.3.2 Model CYD202S Definitions .......................................2-4
2.3.3 Model CYD202D Definitions.......................................2-6
2.4 Sensor Installation Recommendations ..........................2-8
2.4.1 Two-Lead Measurement Considerations....................2-8
2.4.2 Connecting Leads To The Sensor..............................2-8
2.4.3 Sensor Mounting ........................................................2-9
2.4.4 Current Source Dependence....................................2-10
2.4.5 Measurement Errors Due To AC Noise....................2-11
2.5 Sensor Curve Definition ...............................................2-12
2.6 Power Connections ......................................................2-12
2.7 Panel Mounting ............................................................2-13
2.8 Initial Setup and Checkout Procedure .........................2-13
3 OPERATION ................................................................................3-1
3.0 General ..........................................................................3-1
3.1 Temperature Unit Selection ...........................................3-1
3.2 Diode Curve Selection ...................................................3-1
3.3 Blinking Decimal Point ...................................................3-1
3.4 Front Panel Operation....................................................3-2
4 SERVICE......................................................................................4-1
4.0 General ..........................................................................4-1
4.1 General Troubleshooting................................................4-1
4.2 Operating Software Replacement..................................4-1
4.3 PCB Description.............................................................4-3
4.4 Calibration......................................................................4-3
APPENDIX A – CURVE TABLE ........................................................ A-1

Omega Model CYD201/202 User’s Manual
ii Table of Contents
LIST OF ILLUSTRATIONS
Figure No. Title Page
1-1 Model CYD201, 202 Temperature Monitor Series ....................1-3
2-1 Model CYD201 Front Panel ......................................................2-2
2-2 Model CYD201 Rear Panel.......................................................2-3
2-3 Model CYD202S Front Panel....................................................2-4
2-4 Model CYD202S Rear Panel ....................................................2-5
2-5 Model CYD202D Front Panel....................................................2-6
2-6 Model CYD202D Rear Panel ....................................................2-7
4-1 Location of Fuse and Jumpers .................................................4-2
LIST OF TABLES
Table No. Title Page
1-1 Specifications............................................................................1-4
2-1 Effect of Current Variation on Diode Temperature..................2-10
2-2 Typical CY7 dV/dI Values for Selected Temps .......................2-11
A-1 CY7 Diode Standard Curve...................................................... A-1

Omega Model CYD201/202 User’s Manual
Introduction 1-1
CHAPTER 1
INTRODUCTION
1.0 GENERAL
The CYD201, CYD202Series is designed and manufactured in the United
States of America with these features:
• Bright 4-Digit LED Display of Temperature in K or °C
• Temperature Range: 1.4 K to 475 K (–271 °C to 202 °C)
• Resolution of ±0.1 K or °C
• Overall Accuracy with Calibrated Sensor of ±0.25 K
• Standard Temperature Response Curves, Plus Memory
for Precision Curve Option for a Calibrated Sensor
• Sensor Connections made to Screw Terminal Adapter
• Flexible Power Supply Requirement
We welcome comments on this manual. Although we try to keep it error-
free, some may occur. To report an error, describe it briefly and include the
appropriate paragraph, figure, table, and page number. This manual is
subject to change without notice.
1.1 MODEL CYD20X SYSTEM DESCRIPTION
The Model CYD201, CYD202 Temperature Monitors are a microcontroller-
based instrument which measures temperature. It is designed to use CY7
Silicon diode sensors. The Model CYD201 displays the temperature reading
of one diode sensor. The Model CYD202S has two inputs and one display.
The user selects the input to display by means of a front panel switch. The
diode sensors must conform to the same temperature response curve. The
Model CYD202D has two inputs and two displays. The readings of both
diode sensors continuously display. Each sensor can have its own
temperature response curve. See Figure 1-1.
The Model CYD201, CYD202 Temperature Monitors, coupled with the
CY7series diode sensors, offers outstanding performance and advantages
over traditional thermocouple solutions. In the cryogenic temperature range,
the diode sensor offers a much higher signal and better sensitivity,
repeatability, and accuracy than a thermocouple. The CY7 Series sensors
follow the same temperature response curve, Curve 10. In most applications
they are interchangeable with no need to reconfigure monitors.

Omega Model CYD201/202 User’s Manual
1-2 Introduction
Diode sensors come in several packaging formats for easy mounting. Unlike
a thermocouple, the lead wire in a diode measurement is not the active
sensor component; using an additional connector to bring out the sensor
signal from a cryogenic and/or vacuum system does not degrade the
measurement. Finally, the diode sensor does not require any room
temperature compensation.
These units excite the diode sensor with a 10 µA current source. An analog-
to-digital converter reads the sensor voltage and sends the reading to a
microcontroller. The microcontroller uses the selected temperature
response curve stored in memory to convert sensor voltage to temperature.
The computed temperature displays on the bright front panel LED display.
There are several standard temperature response curves.
Mounting the CYD201 is simple since it is packaged in a 1/8 DIN aluminum
panel mount box. The CYD202S and CYD202D Temperature Monitors are
packaged in 1/4 DIN aluminum panel mount boxes.

Omega Model CYD201/202 User’s Manual
Introduction 1-3
CYD201 Temperature MonitorCYD201 Temperature Monitor
°C°C
CYD202S Temperature MonitorCYD202S Temperature Monitor
KK
Sensor ASensor A Sensor BSensor B
°C°C
CYD202D Temperature MonitorCYD202D Temperature Monitor
KK
Channel A
Channel BChannel B
ModelModel
CYD201CYD201
ModelModel
CYD202SCYD202S
ModelModel
CYD202DCYD202D
OmegaOmega
OmegaOmega
OmegaOmega
C-200-1-1.eps
Figure 1-1. Temperature Monitor Series

Omega Model CYD201/202 User’s Manual
1-4 Introduction
Table 1-1. Specifications
THERMOMETRY
Input/Display: Model CYD201 One input, one display
Model CYD202S Two inputs, one display
Model CYD202D Two inputs, two displays
Measurement type: Two-lead
Sensor Type: Silicon Diode
Input Voltage Range: 5 Volts
Sensor Excitation: 10 µA ±0.2%
Temperature Range: 1.4–475 K
Electronic Accuracy with Silicon Diode Sensor:
±0.1 degree typical, ±0.2 degree maximum
Accuracy with Calibrated Sensor: ±0.25 K
Sensor Curves: Curve 10, D-Curve.
DISPLAY
Type: 4-Digit Red LED Display, 14.2 mm
(0.56 in.) high, and unit annunciators
Resolution: 0.1 K or °C
Units: K or °C
Update Rate: 3 updates per second
REAR PANEL CONNECTORS AND SWITCHES
Sensor Input: Screw terminal
Power Input: Power jack accepts power plug compatible to
Switchcraft S-760 or S-765 or screw terminal
Configuration Switch: 4-position DIP Switch to Select Curve and
Temperature Unit
GENERAL
Ambient Temperature Range: 15–35 °C
Power Requirements: 20–35 VDC or 15–24 VAC (50-60 Hz),
3.5 Watts (Maximum)
Size: Model CYD201 = 96 x 48 x 146 mm
(3.78 x 1.89 x 5.75 in.);
Model CYD202S & CYD202D =
96 x 96 x 146 mm (3.78 x 3.78 x 5.75 in.)
Panel Mount Cutout Dimensions:
Model CYD201 = 91 x 44 mm (3.58 x 1.72 in.);
Model CYD202S & CYD202D = 91 x 96 mm
(3.58 x 3.58 in.)

Omega Model CYD201/202 User’s Manual
Installation 2-1
CHAPTER 2
INSTALLATION
2.0 GENERAL
This chapter covers Inspection and Unpacking (Paragraph 2.1), Repackaging
for Shipment (Paragraph 2.2), Front and Rear Panel Definitions (Paragraph
2.3), Sensor Installation Recommendations (Paragraph 2.4), Sensor
Definitions (Paragraph 2.5), Power Connections (Paragraph 2.6), Panel
Mounting (Paragraph 2.7), and Initial Setup and Checkout (Paragraph 2.8)
2.1 INSPECTION AND UNPACKING
Inspect shipping containers for external damage. Make all claims for
damage (apparent or concealed) or partial loss of shipment in writing to
Omega Engineering within five (5) days from receipt of goods. If damage or
loss is apparent, please notify the shipping agent immediately.
Open the shipping containers. Use the packing list included with the system
to verify receipt of the instrument, sensor, accessories, and manual. Inspect
for damage. Inventory all components supplied before discarding any
shipping materials. If there is freight damage to the instrument, file proper
claims promptly with the carrier and insurance company and notify Omega
Engineering. Notify Omega immediately of any missing parts. Omega
cannot be responsible for any missing parts unless notified within 60 days of
shipment.
2.2 REPACKAGING FOR SHIPMENT
To return the unit or accessories for repair or replacement, obtain a Return
Authorization (RA) number from Customer Service in the United States.
Instruments may not be accepted without a RA number. When returning an
instrument for service, Omega must have the following information before
attempting any repair.
1. Instrument model and serial number.
2. User name, company, address, and phone number.
3. Malfunction symptoms.
4. Description of system.
5. Return Authorization (RA) number.
Repack the system in its original container (if available). Affix shipping
labels and FRAGILE warnings. Write RA number on the outside of the
container or on the packing slip. If not available, consult Omega for shipping
and packing instructions.

Omega Model CYD201/202 User’s Manual
2-2 Installation
2.3 FRONT AND REAR PANEL DEFINITIONS
This paragraph defines front and rear panels of the Model CYD201
(Paragraph 2.3.1), Model CYD202S (Paragraph 2.3.2), and Model
CYD202D (Paragraph 2.3.3).
2.3.1 Model CYD201 Definitions
The Model CYD201 has no front panel controls. The 4-digit red LED
displays the temperature in Kelvin (K) or degrees Celsius (°C). Select
temperature units with the rear panel DIP switch. See Figure 2-1.
CYD201 Temperature MonitorCYD201 Temperature Monitor
°C°C
OmegaOmega
C-200-2-1.eps
Figure 2-1. Model CYD201 Front Panel
The rear panel consists of the 24 Volt power input connector, DIP Switch,
CAL trimpot, and screw-terminal connector. See Figure 2-2.
24 Volt Power Input Connector. The line cord from the wall mounted
power supply has a power plug that inserts into the Model CYD201 rear
panel. The Model CYD201 is off when not plugged in, and on when plugged
in. Make sensor connections before applying power to the instrument.
DIP Switch. The DIP switch controls temperature display and curve
selection. The first switch, labeled K/C, selects Kelvin or degrees Celsius for
display. The next two switches select the proper sensor curve as shown in
the table below. The four curve types are defined in Paragraph 2.5. The
fourth switch is not used.
CURVE 1 CURVE 0 SETTING
OPEN
OPEN
CLOSE
CLOSE
OPEN
CLOSE
OPEN
CLOSE
CY7
CTI-Curve
D-Curve
Precision Option

Omega Model CYD201/202 User’s Manual
Installation 2-3
Model CYD201 Definitions (Continued)
CAL Trimpot. The CAL trimpot adjusts instrument calibration. Refer to
Paragraph 4.4 for details.
Screw-Terminal Connector. The diode terminals are marked +for the
anode and –for the cathode. VREF and Shield are used during unit
calibration. Refer to Paragraph 4.4 for details. Shield also terminates the
diode sensor cable shield. Finally, the power for multiple units can be
ganged together to a common on/off switch using the Optional Power input,
which is the first two inputs on the screw-terminal connector. This is an input
only, and can not be used as a voltage tap.
PO ERPO ER
2424 CALCAL
2424
PO ERPO ER
OPTIONALOPTIONAL
SHIELDSHIELD
K / CK / C
CURVE 1CURVE 1 CURVE 0CURVE 0
11223344
- - - OPEN - - -- - - OPEN - - -
VREFVREF
C-200-2-2.eps
Figure 2-2. Model CYD201 Rear Panel

Omega Model CYD201/202 User’s Manual
2-4 Installation
2.3.2 Model CYD202S Definitions
The Model CYD202S has one front panel control. The Sensor A/Sensor B
switch selects which sensor data to display. Both sensors must conform to
the same temperature response curve. The 4-digit red LED displays the
selected temperature in Kelvin (K) or degrees Celsius (°C).
CYD202S Temperature MonitorCYD202S Temperature Monitor
KK
Sensor ASensor A Sensor BSensor B
OmegaOmega
C-200-2-3.eps
Figure 2-3. Model CYD202S Front Panel

Omega Model CYD201/202 User’s Manual
Installation 2-5
Model CYD202S Definitions (Continued)
The Model CYD202S rear panel is the same as the Model CYD201 except:
The upper screw-terminal connector applies to Sensor A. The lower screw-
terminal connector applies to Sensor B. The front panel switch selects
between the two sensors. Both sensors must conform to the same
temperature response curve selected by the CURVE 1 and CURVE 0
DIP switches. There is only one POWER connector and DIP Switch (refer to
Paragraph 2.3.1).
PO ER
2424 CAL
24
PO ER
OPTIONAL
VREF
SHIELD
SHIELD NC NC NC
Sensor A
Sensor BSensor B
K / CK / C
CURVE 1
CURVE 0CURVE 0
11223344
- - - OPEN - - -- - - OPEN - - -
C-200-2-4.eps
Figure 2-4. Model CYD202S Rear Panel

Omega Model CYD201/202 User’s Manual
2-6 Installation
2.3.3 Model CYD202D Definitions
The Model CYD202D has no front panel controls. Two 4-digit red LEDs
simultaneously display temperatures in Kelvin (K) or degrees Celsius (°C).
In essence, the Model CYD202D operates as two independent units with a
common power supply.
°C°C
CYD202D Temperature MonitorCYD202D Temperature Monitor
K
Channel A
Channel B
Omega
C-200-2-5.eps
Figure 2-5. Model CYD202D Front Panel

Omega Model CYD201/202 User’s Manual
Installation 2-7
Model CYD202D Definitions (Continued)
Descriptions of the Model CYD202D rear panel are the same as the Model
CYD201 except two complete sets of DIP switches (refer to Paragraph
2.3.1), CAL trimpots, and screw-terminal connectors are provided. The
upper set applies to Channel A. The lower set applies to Channel B. The
unit simultaneously displays the temperatures of both sensors. There is only
one POWER connector.
CALCAL
VREFVREF
SHIELDSHIELD
PO ERPO ER
2424 CALCAL
2424
PO ERPO ER
OPTIONALOPTIONAL
VREFVREF
SHIELDSHIELD
NCNC NCNC
Channel AChannel A
Channel BChannel B
K / CK / C
CURVE 1CURVE 1 CURVE 0CURVE 0
11223344
- - - OPEN - - -- - - OPEN - - -
K / CK / C
CURVE 1CURVE 1 CURVE 0CURVE 0
11223344
- - - OPEN - - -- - - OPEN - - -
C-200-2-6.eps
Figure 2-6. Model CYD202D Rear Panel

Omega Model CYD201/202 User’s Manual
2-8 Installation
2.4 SENSOR INSTALLATION RECOMMENDATIONS
Abbreviated sensor installation recommendations for the Model CYD201 are
included in this section. Please refer to the Omega Product Catalog for
sensor specifications. Call Omega for copies of application notes or with
questions or comments concerning sensor installation.
1. Do not ground the sensor.
2. Shield leads and connect shield wire to SHIELD on screw terminal
connector only. Do not connect shield at other end of cable.
3. Keep leads as short as possible.
4. Use twisted-pair wire. Use Omega Duo-Twist™ wire (or equivalent) for
two-wire, or Quad-Twist™ wire (or equivalent) for four-wire applications.
5. Thermally anchor lead wires.
2.4.1 Two-Lead Measurement Considerations
In two-lead measurement, the leads measuring sensor voltage are also the
current carrying leads. The resultant voltage measured at the instrument is
the sum of the temperature sensor voltage and the IR voltage drop within
the two current leads. In a cryogenic environment, the heat flow down the
leads is of critical concern, so wire of small diameter and significant
resistance per foot is preferred to minimize heat flow. Consequently, a
voltage drop within the leads may exist.
Expect some loss in accuracy since the voltage measured at the voltmeter
is the sum of the sensor voltage and the voltage drop across the connecting
leads. The exact measurement error depends on sensor sensitivity and
variations resulting from changing temperature. For example, a 10 Ωlead
resistance results in a 0.1 mV voltage error. The resultant temperature error
at liquid helium temperature is only 3 mK, but because of the lower
sensitivity (dV/dT) of the diode at higher temperatures, it becomes 10 mK at
liquid nitrogen temperature.
2.4.2 Connecting Leads To The Sensor
Excessive heat flow through connecting leads to any temperature sensor
may differ the temperature between the active sensing element and the
sample to which the sensor mounts. This reflects as a real temperature
offset between what is measured and the true sample temperature.
Eliminate such temperature errors with proper selection and installation of
connecting leads.
To minimize heat flow through the leads, select leads of small diameter and
low thermal conductivity. Phosphor-bronze or Manganin wire is commonly
used in sizes 32 or 36 AWG. These wires have a fairly low thermal
conductivity, yet electrical resistance is not large enough to create
measurement problems.

Omega Model CYD201/202 User’s Manual
Installation 2-9
Connecting Leads To The Sensor (Continued)
Thermally anchor lead wires at several temperatures between room
temperature and cryogenic temperatures to guarantee no heat conduction
through the leads to the sensor.
2.4.3 Sensor Mounting
Before installing a diode sensor, identify which lead is the anode and which
is the cathode. When viewed with the base down and the leads towards the
observer, the anode is on the right and the cathode is on the left. The silicon
diode sensor lead configuration is shown to the right. For other sensors,
read accompanying literature or consult the manufacturer to positively
identify sensor leads. Lead identification should remain clear even after
sensor installation. Record the sensor serial number and location.
CY7-SD
Diode Sensor Leads
Anode
Cathode
On the CY7-SD, the base is the largest flat surface. It is sapphire with gold
metalization over a nickel buffer layer. The base is electrically isolated from
the sensing element and leads; make all thermal contact to the sensor
through the base. A thin braze joint around the sides of the SD package
electrically connect to the sensing element. Avoid contact to the sides with
any electrically conductive material.
When installing the sensor, make sure there are no electrical shorts or
current leakage paths between the leads or between the leads and ground.
If IMI-7031 varnish or epoxy is used, it may soften varnish-type lead
insulations so that high resistance shunts appear between wires if sufficient
time for curing is not allowed.
Slide Teflon®spaghetti tubing over bare leads when the possibility of
shorting exists. Avoid putting stress on the device leads and allow for
thermal contractions that occur during cooling which could fracture a solder
joint or lead if installed under tension at room temperature.
For temporary mounting in cold temperature applications, apply a thin layer
of Apiezon®N Grease between the sensor and sample to enhance thermal
contact under slight pressure. The preferred method for mounting the
sensor is the Omega CO Adapter.

Omega Model CYD201/202 User’s Manual
2-10 Installation
Sensor Mounting (Continued)
CAUTION: Omega will not warranty replace any device damaged by user-
designed clamps or solder mounting.
For semi-permanent mountings, use Stycast epoxy instead of Apiezon®N
Grease.
NOTE: Do not apply Stycast epoxy over the CY7-SD package--sensor
stress may shift the readings. In all cases, periodically inspect the sensor
mounting to verify good thermal contact to the mounting surface is
maintained.
2.4.4 Current Source Dependence
This paragraph addresses the effects of current source accuracy on
temperature measurement accuracy. Although the Model CYD201 has an
accurate internal current source, it is important to understand the
relationship between current variation and measurement accuracy.
Diode sensors possess a non-linear forward current-voltage characteristic.
Consequently, the forward voltage variation with changing current for diodes
is smaller than for resistance temperature sensors, which have linear
current-voltage characteristics.
Below 30 K, the sensitivity (dV/dT) of Omega Engineering diode
temperature sensors increases by an order of magnitude over sensitivities
at higher temperatures. The slope (dV/dI) of the I-V curves stays relatively
constant. Both characteristics reduce even further the effect of any change
in forward bias current on temperature measurement accuracy. Refer to
Tables 2-1 and 2-2.
Table 2-1. Effect of Current Variation
on Diode Temperature Measurement Accuracy
T (K) ∆
∆∆
∆I, µA* Acc. (%)* Range (µA)* Error (K)
300
0.5
0.05
0.005
5
0.5
0.05
9.5 to 10.5
9.95 to 10.05
9.995 to 10.005
1
0.1
0.01
150
1
0.1
0.01
0.005
10
1
0.1
0.05
9 to 11
9.9 to 10.1
9.99 to 10.01
9.995 to 10.005
1
0.1
0.01
0.005
50
3
0.3
0.03
0.005
30
3
0.3
0.05
7 to 13
9.7 to 10.3
9.97 to 10.03
9.995 to 10.005
1
0.1
0.01
0.005
* With current source (I≈10 µA).

Omega Model CYD201/202 User’s Manual
Installation 2-11
Current Source Dependence (Continued)
If the output from a current source is not precisely 10 µA, the error in
temperature can be calculated by this relationship between the dV/dT and
dV/dI values: DT = (DI • dV/dI) / (dV/dT)
Note values dV/dI and dV/dT are derived at same temperature (T).
Table 2-2. Typical CY7 dV/dI Values for Selected Temperatures
T (K) dV/dI (approx.)
300
77
4.2
3000 Ω
1000 Ω
2800 Ω
2.4.5 Measurement Errors Due To AC Noise
Poorly shielded leads or improperly grounded measurement systems can
introduce AC noise into the sensor leads. In diode sensors, the AC noise
shifts the DC voltage measurement due to the diode non-linear
current/voltage characteristics. When this occurs, measured DC voltage is
too low and the corresponding temperature reading is high. The
measurement error can approach several tenths of a Kelvin. To determine if
this problem exists, perform either procedure below.
1. Place a capacitor across the diode to shunt induced AC currents.
Capacitor size depends on the noise frequency. If noise is related to
power line frequency, use a 10 microfarad capacitor. If AC-coupled
digital noise is suspected (digital circuits or interfaces), use a 0.1 to 1
microfarad capacitor. In either case, if measured DC voltage increases,
there is induced noise in the measurement system.
2. Measure AC voltage across the diode with an AC voltmeter or
oscilloscope. Most voltmeters do not have the frequency response to
measure noise associated with digital circuits or interfaces (which
operate in the MHz range). For a thorough discussion of this potential
problem, and the magnitude of error which may result, request the
paper “Measurement System-Induced Errors In Diode Thermometry,”
J.K. Krause and B.C. Dodrill, Rev. Sci. Instr. 57 (4), 661, April, 1986
from Omega.
To greatly reduce potential AC noise, connect twisted leads (pairs) between
the measurement instruments and the diode sensors. Use 32 or 36 AWG
Omega Engineering Duo-Twist™ Cryogenic Wire, which features phosphor
bronze wire twisted at 3.15 twists per centimeter (8 twists per inch).

Omega Model CYD201/202 User’s Manual
2-12 Installation
2.5 SENSOR CURVE DEFINITION
Sensor curves available with the Model CYD201 include Curve 10,
CTI-Curve, D-Curve, and a factory installed Precision Option for a calibrated
sensor. After selecting the proper curve, set the Model CYD201 rear panel
DIP switch (refer to Paragraph 3.2).
Curve 10. CY7 Series silicon diodes follow the same standard temperature
response Curve 10 and are interchangeable. Curve 10 is programmed into
all Omega Temperature Controllers, digital thermometers, and temperature
monitors. Silicon Diode Series sensors come in five bands of tracking
accuracy.
Forward Voltage  V
f
(volts)
1.
1.6
1.4
1.2
1.0
0.
0.6
0.4
0.2
020 60 200 300
Temperature, K (kelvin)
Standard Curve 10
100 20 3040 5060
Average
Slope
26 mV/K
Average
Slope
2.3 mV/K
2.6 POWER CONNECTIONS
The Model 200 accepts a broad power supply AC or DC voltage range from
any polarity power supply. If the Model CYD201 is ordered with a wall-mount
power supply, a 24 Volt AC power supply is included. The line cord from the
wall mounted power supply has a power plug that inserts into the 24 Volt
Connector on the rear panel. The unit is off when not plugged in, and on
when plugged in. Make sensor connections before applying power to the
instrument.
The power for multiple Model CYD202S can be ganged together to a
common on/off switch using the Optional 24-Volt Power Input, being the first
two inputs on the screw-terminal connector. This is an input only, and
should not be used as a voltage tap.