Watlow SBL Card User Manual

Power Controls

Watlow Controls, 1241 Bundy Blvd.,

P.O. Box 5580, Winona, MN 55987-5580

Phone: [phone], Fax: [phone]

SBL Card

Specifications

• Power Requirements: 4-20mA DC current.

Temperature controls must provide at least

7.5VDC (375Ω SBL input impedance).

• Linearity: Within ± 3% over a 20 to 80% power
region.

• Operating Temperature: 32 to 122°F/ 0 to 50°C
0 to 90% RH, non-condensing.

• Firing Mode: Variable Time Base @ 50% power,
3 cycles ON, 3 cycles OFF, zero-cross switching
with 1/2 cycle resolution.

• Output: 3.5VDC minimum. Current is dependent
upon the SSR input impedance.

Dimensions

SBL

08-5399

General Description

The Watlow SBL card is a stand-alone control card
which accepts a proportional 4-20mA command
signal from a temperature control. It provides a
variable time-base, proportional output for a zero
cross-fired, DC input solid state relay (SSR). The
SBL can drive one SSR for single phase or two
SSRs for three-phase, two-leg applications. The
SBL is loop powered from the 4-20mA, so there is
no need for an external power supply. It easily
attaches to the SSR input terminals, making it a
compact power control with a variety of voltages and
amperages limited only by the SSR’s output.

2.0"

(51 mm)

Bias Gain

-+

2.67"

(68 mm)

ON

Setup Procedure

1. Set the temperature control command signal to
20mA.

2. Adjust the Gain potentiometer until the SSR
output is just full ON (LED full on).

3. Set the temperature control command signal to
4mA.

4. Adjust the Bias potentiometer for ZERO output at
4mA (LED full off).

5. Repeat Steps 1 through 4 until no further
adjustment is required.

WSBL-XDSN Rev A00
January, 1996

SBL Card Data Sheet 1

Wiring Diagrams

Troubleshooting

L2

L1

Limit Contactor

( If Required)

∫∫

∫

∫∫

Semiconductor

Fuse

Contacts

SBL

4-20mA Input

Heater

SSR

Output

SSR
Input

+-

-+

ON

LED

Single Phase

WARNING: Wiring examples show L2 in
240V~ (VAC) or 480V~ (VAC) configuration.
In 120V~ (VAC) or 277V~ (VAC) applications,
L2 is neutral and must not be fused or
switched. Failure to follow this guideline
could result in death or personal injury.

Symptom • No Output
Possible Causes • No command signal

• No VAC to the heater

• Blown fuse

• Defective SSR

• Defective SBL

• Impedance mismatch

between temperature
control and SBL input

Troubleshooting Procedure

1. Make sure the “ON” LED located on the SBL card
is cycling or full ON. If not, check the 4-20mA
command signal. The SBL card requires at least
5mA to cycle. The SBL will not accept a voltage

input.

2. If the 4-20mA command signal is good and the
LED is cycling or full ON, check for VAC to the
heater. First, remove AC power from the system.

Proceed with caution. The

∫∫

∫

∫∫

WARNING:
remainder of step #2 has a potential shock

hazard. This is high voltage and is electrically
hot (120VAC or greater). Only qualified
electrical personnel should continue with
the remainder of this procedure.

NOTE: The SBL Card can operate a maximum of 2
SSR's wired for 3 phase-2 leg control.

L1
L2
L3

Limit

Contactor

Contacts

( If Required)

Semiconductor

Fuses

SBL

4-20mA

SSR

Output

_

SSR
Input

+-

+

ON

LED

Heater

_

SSR

Output

SSR

Input

Next, using an AC voltmeter, connect the volt­meter leads across the heater terminals and
reapply power with the command signal at 20mA.
If there is no voltage present, remove power and
check for a blown fuse. To check for a blown fuse,
either replace the fuse, or measure it with an
ohmmeter and replace if necessary. The
ohmmeter should read around 0 ohms.

3. If the fuse is good, measure the voltage across the
terminals where the temperature control and SBL
connect. It should be 7.5 VDC minimum with the
input signal at 20mA. If the voltage is less, there
is probably an impedance mismatch between the
temperature control and SBL.

A quick way to check for an impedance mismatch
is to disconnect the SBL from the temperature

+

control. Replace the SBL with a 375Ω resistor,
and set the input signal to 20mA. Measure the
voltage across the resistor; it should be 7.5VDC
minimum. If the voltage is less than 3.5VDC @
4mA input signal, the SBL is defective and should
be returned for repair or replacement.

Three Phase, Two Leg

2 SBL Card Data Sheet

If the LED works on the SBL, but the SSR will not
turn on, there may be a mismatch between the
SBL and SSR. Try a different SSR.