Chapter 4 – Temperature Controller
TestEquity TEC1 Thermoelectric Temperature Chamber
Page 4-7
GPIB and Ethernet Programming
Floating Point Variables
EZ-Zone PM Series controllers use two consecutive register to control a value or to read back a
process variable. The two registers hold an IEEE-754 32-bit floating point word. The registers
are read and written to in the low word-upper word order.
Floating Point Write
The WF command writes the num value in floating point format to two consecutive registers
starting with the low word register.
To enter a temperature setpoint:
WF 2160, 50
'writes 50.0°C to registers 2160 and 2161
WF 2160, 15.5
'writes 15.5°C to registers 2160 and 2161
Floating Point Read
The RF? query reads a 32-bit floating point value from two sequential register in low word-upper
word order. The RF? does not require the number of register to read since it is fixed at two
registers.
To read the actual chamber temperature:
RF? 360
'reads registers 360 and 361
The [?] is an optional symbol for smart programs like ICS’s GPIBKybd program. These
programs can recognize the command as a query and automatically read the response.
Setting Modbus Device Timeouts
The time that the 4899A/8099 waits to receive a response from the Modbus device is
programmable by the D command. This is an internal 4899A/8099 timeout and not the same as
the GPIB bus timeout. If the 4899A/8099 does not receive a response within the timeout period,
it assumes that the Modbus device is not responding and sets the timeout error. Timeout errors
can be determined by reading the 4899A/8099’s Modbus Error Register with the E? query. If the
error code is 101 (Modbus timeout) then the timeout period should be lengthened. The command
to change the timeout period is:
D 300
‘
sets timeout period to 300 ms
*SAV 0
‘saves current values and configuration (do this if you want to keep
the new value)
The default time period of 100 milliseconds has proved to be satisfactory for most applications.
The recommendation is that your program should have a built-in recovery routine to handle the
possibility of a timeout error.
More details on GPIB and Ethernet Interface
See the ICS Electronics Manual for more details on the GPIB or Ethernet interfaces.